This study proposes a disturbance observer-based proportional-type DC-link voltage tracking algorithm for permanent magnet synchronous generators (PMSGs). The proposed technique feedbacks the only proportional term of the tracking errors, and it contains the nominal static and dynamic feed-forward compensators coming from the first-order disturbance observers. It is rigorously proved that the proposed method ensures the performance recovery and offset-free properties without the use of the integrators of the tracking errors. A wind power generation system has been simulated to verify the efficacy of the proposed method using the PSIM (PowerSIM) software with the DLL (Dynamic Link Library) block.

Because of the high efficiency, high power, and simple structures, the use of permanent magnet synchronous machines (PMSMs) for various motoring and generating applications has been preferred. Eliminating the external rotor excitation removes the rotor losses, which improves the PMSM efficiency dramatically. Moreover, the absence of rotor winding eliminates not only the slip rings but also the brushes, which leads to a considerable reduction of the maintenance costs [

In power generating applications, the PMSM plays the role of a balanced three-phase AC power supply depending on the input mechanical power source, such as wind power, thermoelectric power, nuclear power, and so on. The DC-link voltage across the output capacitor should be controlled by the three-phase inverter with properly designed control algorithms. Because the corresponding DC-link voltage control problem of the PMSM-based power system is equivalent to the case of the AC/DC converter with a variable AC power source, the extant solutions for the AC/DC converter output voltage control problems can be applied. The cascade control strategy has mainly been adopted for controlling the output voltage of AC/DC converters, where the outer-loop controller produces a desired

There have been many multi-variable approaches in [

This paper offers a DOB-based proportional-type DC-link voltage tracking algorithm, considering the nonlinearity in the DC-link voltage and PMSM dynamics with the model-plant mismatches. The proposed method is derived through a multi-variable approach, which combines the simple proportional-type feedback linearizing (FL) controller with the first-order DOBs. The contribution of this article is summarized as follows. First, it incorporates the first-order DOBs in the proportional-type FL DC-link voltage control algorithm so as to stabilize the tracking errors. Second, it is rigorously proved that the closed-loop system ensures the performance recovery property as well as the offset-free property without the use of the integrators of the tracking errors. The realistic simulation results confirm the efficacy of the proposed method, in which the wind power system with the output capacitor has been emulated by PSIM (PowerSIM) software.

In the rotational

Letting

It should be noted that it is difficult to consistently identify the true values of the PMSG parameters, with the exception of the number of pole pairs

The next section develops a DC-link voltage tracking algorithm based on the perturbed PMSG current dynamics of Equations (

The disturbances

The stationary

The DC-link voltage control objective is to force the closed-loop system to behave according to the transfer function given by

The time domain expression of the target dynamics of Equation (

The stabilization of the tracking error dynamics of Equation (

The state

Substitution of the proposed

The result of Lemma 1 implies that the DC-link voltage of

The next step is to derive the

For stabilizing the error dynamics of Equations (

Substituting the control laws of Equations (

The result of Lemma 2 implies that the

Now, it is ready to analyze the closed-loop tracking error behaviors by using two inequalities of Equations (

Note that it is not clear whether the closed-loop system suffers the offset errors or not in the real implementations, as the proposed control algorithms of Equations (

This section discusses the simulations to show the efficacy of the proposed method, comparing this with the classical feedback linearizing method in [

The cut-off frequencies were adjusted as

The FL technique in [

Here, the

The first simulation was conducted to evaluate the DC-link voltage tracking performance with a resistive load of

The second simulation compared the DC-link voltage regulation performances by applying the pulse resistive load from

The third simulation was performed to show the closed-loop robustness by investigating the DC-link voltage tracking performance variations for different load conditions, such as

In the last simulation, the DC-link voltage tracking behaviors were compared at a resistive load of

As shown in the simulation results, in contrast to the classical FL method, the proposed method successfully maintains a satisfactory closed-loop performance despite the operating mode changes. Hence, the proposed method offers almost the same closed-loop performance for various operating ranges without any additional gain scheduling method, which corresponds to a practical advantage of the proposed technique.

In this article, a robust DC-link voltage tracking algorithm was proposed by incorporating first-order DOBs in the proportional-type feedback-linearizing DC-link voltage control algorithm. It is rigorously shown that the proposed method guarantees the performance recovery property with the offset-free property. The efficacy of the proposed method has been confirmed by performing realistic simulations for wind power system applications.

This research was supported by the newly created professor research fund of Hanbat National University in 2017.

The authors declare no conflict of interest.

This section proves Lemmas 1 and 2, and Theorems 1 and 2 in a sequential manner. First, Lemma 1 is proved as follows.

The nonlinear observer of Equation (

Now, consider the positive definite function defined in Equation (

It is easy to see that the positive constant

The proof of Lemma 2 is given as follows.

The nonlinear observers of Equations (

Now, consider the positive definite function defined in Equation (

Theorem 1 is proved as follows.

Define the composite-type positive definite function as

The proof of Theorem 2 is given as follows.

As can be seen in the proof of Theorem 1 in the

Because the matrix

Equation (

The permanent magnet synchronous generator (PMSG) power system topology.

The implementation of the closed-loop system

The closed-loop performance comparison between the proposed method and the feedback linearizing (FL) method with a resistive load of

The estimated disturbance behaviors and the wind pattern based on the Weibull distribution.

The comparison result of DC-link voltage regulation performance between the proposed method and the feedback linearizing (FL) method at the DC-link voltage of 300 V with a pulse resistive load torque from

The permanent magnet synchronous generator (PMSG) output power behaviors of the proposed method and the feedback linearizing (FL) method at the DC-link voltage of 300 V with a pulse resistive load torque from

The DC-link voltage tracking performance variation comparison between the proposed method (

The DC-link voltage tracking behavior comparison between the proposed method (