Matlab/Simulink 2020. Many reasons cause fluctuations in a DC supply such as loose, corroded connections, or

unregulated supply. The paper proposes a solution for fluctuations in DC supply of three phase voltage source

inverter using two degree of freedom controllers Feeback (FB) and Feedforward (FF). The results show that FB

only can't solve the disturbances and sudden jumps of the DC voltage. Using both controllers FB and FF solve

this problem and the performance such as overshoot, rise time, peak time, and settling time parameters are

improved under different load conditions for ±15% fluctuation in DC supply

Key-Words:- Intelligent Controller, Fluctuations, Three-phase inverter, Feedback Controller,

Feedforward controller.

input tracking under sudden grid input change are

needed to enhance AC machine drive system.

Feedback controller can be used to improve input

tracking, but it can’t solve disturbance and system

noise problem coming from sudden change in the

DC grid input. Using both feedforward and

feedback controllers enhance the AC drive system

and decrease the effect of grid input fluctuation and

noise.

In [1], the authors presented a multi-path

the technique suggested based on the assumption

that it would reduce system impedance to avoid

voltage drop.

feedforward circuit to generate improvements that

help the grid's capability, effectively solving high-

frequency current harmonics when The LCL filter

exists in a weak grid linked with an inverter. these

harmonics caused malformation in system current,

experimental and theoretical interpretation of

outcomes confirmed by the modeling and results

obtained.

converter applications by utilizing low-bandwidth

connections. It seems that in low-frequency, both

control feedforward and feedback have the same

behavior, but at high frequency, feedforward

became an active filter that raises system input

stability as in [5].

The Control and stabilizing systems for both

VSC and CSC have been discussed elaborately. The

transient response and the best steady-state

especially important in a grid-interfacing converter

system.

The grid current harmonics issue could be

solved using the feedforward approach under the d-

q rotating frame, these harmonics caused by the

distortion from grid voltage in the grid tide inverter

(voltage source inverter) with LCCL filter. Both

simulations and experiments have substantiated the

efficacy of this approach. This novel approach

a control reference in grid-connected inverter with

LCL filter [8], where the voltage feedforward

mainly uses the continuous controller. The

continuous approach cannot be applied to discrete

controllers because it relies on grid voltage as a

feedforward control strategy. Hence, the author

suggests the full grid-voltage feedforward that

conceivably uses in the discrete state-space

author suggests the Passivity-Based Stability

Criterion (PBSC) by passivity dominant on the DC

bus, where The Performance and stability ensure

with a passivity criterion, where the simulation has

been using to clarify this theory; in the end, the

paper offers a summary of the research on these

various stability studies.

[14] presented that, the grid voltage feedforward

A detailed description for simulating a three-

phase voltage source with dSPACE 1104 control

circuitry will allow future use of dSPACE

Controller in photovoltaic projects is introduced in

[15]. There is a substantial improvement in the

inverter voltage output. As stated in this paper, this

controller can be built using the dSPACE board as a

design tool. The model provides a 2.83% total

harmonic distortion value rather than approximately

connected inverter with LCL filter is presented in

[16]. The author proposed a scheme able to control

three reference frames (stationary, synchronous,

decupled synchronous) rather than the proportional

feedforward. the Transient response to changing

further limits by feedforward signal amplitude; the

results obtained show that the suggested

feedforward schemas are effective.

[17] presented the outstanding result for The

transformer after the filter(LC) to obtain the

compact size.

The author proposed in [18] a control technique

for a three-phase grid-connected inverter in a PV

the mathematical model built, and the case applied

to a 5KW solar cell system that This control strategy

Figure 2 illustrates the overall MATLAB/Simulink system.

The output of three phase inverter is shown in

Figure 3.

Fig. 3: Fundamental waveforms.

In this control system, the set point voltage

(V_SP) was the only reference to generate the

required pulses and the voltage waveform.

After that step, the controller using the tuned

output is within the required boundary. Moreover,

the pulse generator sensed the features of the three-

phase reference waveforms and provided an

appropriate six pulses to the inverter switching

devices.

load case with a full-load case with DC link voltage

disturbance, this compression made by three cases

each case have DC link disturbance signal at 15%

the anlayzed data contains the main properties of

the figures [ Rise time, Settling time, Settling Min,

Settling Max, Over shoot, Under shoot, Peak ,Peak

time], Figure 5 illustrate the shape of DC link

Table 1 will be used, then the disturbance of DC

link input is -15% around the set point will be

applied.

The first negative edge analysis from Figures (10-

13) and Table 3 proved that load increment has a

positive effect on the rise time and overshoot

values, and at the same time it has a negative effect

on the settling time. It is also noticeable that the

proposed control system (FB+FF) overcame the

and Table 4 showed that load increment has a

positive effect on the rise time and the settling time,

and at the same time it has a negative effect on the

overshoot values.

Fig. 14: Output voltage responses at 15%

disturbance - No load condition.

Fig. 15: Error signals of both controllers at 15%

Fig. 18: overall system Output voltage responses at

15% disturbance - No load condition.

The error signal of both control system under

no load condition were shown in Figure 19. The

Fig. 19: Error signals of both controllers at 15%

disturbance - No load condition.

Figure 20 illustrated the modulation index

performance of both systems under no load

condition. It can be observed that the relation

between the DC link voltage and the modulation

index is inverse one. Moreover, the proportional

Fig. 20: Modulation indexes of both controllers at

15% disturbance - No load condition.

disturbance - No load condition.

Figure 24 explained the feedforward/feedback

controller behaviour under various conditions (10%

and 15% disturbances at different load conditions).

It can be observed that the controller performed

better responses at full load conditions, in spite of

the disturbance increment. In order to achieve that

in the case of full load condition, the modulation

Fig. 25: Modulation index responses of FF/FB

control with different loading – disturbances.

The speed response of the proposed controller

under full load condition was illustrated in Figure

26, It can be seen that the speed oscillation was

reduced in small time in both loading cases.