# A Comprehensive Review on Grid Connected Photovoltaic Inverters, Their Modulation Techniques, and Control Strategies

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## Abstract

**:**

## 1. Introduction

## 2. Classification of Inverters

#### 2.1. Line Commutated Inverter

#### 2.2. Self Commutated Inverter

#### 2.2.1. Current Source Inverter

#### 2.2.2. Voltage Source Inverter

## 3. Configuration of PV Inverters

#### 3.1. Central Inverter

#### 3.2. String Inverter

#### 3.3. Multi-String Inverter

#### 3.4. Module Integrated or AC Module

## 4. Multi-Level Inverter Topologies

#### 4.1. Neutral Point Clamped GCMLI (NPC-GCMLI)

_{1}and D

_{2}), 04 switches (S

_{1}, S

_{2}, S

_{3}, and S

_{4}), and 02 capacitors (C

_{1}and C

_{2}). This inverter can attain 03 voltage level (0, +V

_{dc}/2, and −V

_{dc}/2) at the output. A 0 level is attained by turning ON S

_{2}and S

_{3}, a value of +V

_{dc}/2 is accomplished in a case when S

_{2}and S

_{1}are in ON state, and a voltage level of −V

_{dc}/2 is attained by turning ON S

_{3}and S

_{4}[53]. Moreover, due to its modular structure, it can be expended easily for high power ratings. A detailed analysis of a 5-level NPC presented in [55] utilizes eight switches, 04 DC-link capacitors, and 06 free-wheeling diodes to achieve five voltage levels at the output. The capacitance requirement in this topology is low as it shares a common DC bus, makes it lightweight. However, the main disadvantage in NPC topology is that the complexity to balance the DC-link capacitor increases with the increment in the number of levels. Therefore, a proper DC-link voltage regulation is required to balance the DC-link. NPC is widely used in grid-connected applications due to fast dynamic response, small leakage current, simple structure, and high efficiency [56].

#### 4.2. Flying Capacitor GCMLI (FC-GCMLI)

_{1}and C

_{2}), utilizes 04 switches (S

_{1}, S

_{2}, S

_{3}, and S

_{4}), and 01 auxiliary capacitor (C

_{0}) and can achieve 03 levels (0, +V

_{dc}/2, and −V

_{dc}/2) at the output. A voltage level of +V

_{dc}/2 is attained when S

_{1}and S

_{2}are turned ON, and a −V

_{dc}/2 is accomplished by turned ON S

_{3}and S

_{4}. While a 0 voltage level can be achieved when either S

_{2}and S

_{4}or S

_{1}and S

_{3}are turned ON [54]. As the researchers in [58], utilize 08 switches, 04 DC-link, and 06 auxiliary capacitors to attain the 05 voltage levels at output. However, this topology has high installation cost and has low efficiency due to high switching losses. Just like NPC-GCMLI, this topology also has a high modularity in structure and can be expended easily.

#### 4.3. Cascaded H-Bridge GCMLI (CHB-GCMLI)

_{dc}/2, and −V

_{dc}/2). +V

_{dc}and −V

_{dc}voltage levels are accomplished by turning ON S

_{1}and S

_{4}, and S

_{2}and S

_{3}, respectively. However, the voltage at the output port of the inverter is achieved by turning ON either S

_{3}and S

_{4}or S

_{1}and S

_{2}respectively. Furthermore, a 05 level CHB-GCMLI is formed by connecting two 1-Φ H-bridge modules in a series manner as presented in Figure 6c. As 05 level CHB topology is the combination of series connected 02 H-bridges; therefore, the inverter output will be the summation of individual H-bridge output i.e., V

_{out}= V

_{a}

_{1}+V

_{a}

_{2}. Due to its scalable feature and high structure modularity, it can easily be expended to accomplish high voltage levels just by connecting a 1-Φ H-bridge module in series. Moreover, CHB topology is compact as compared to NPC and FC due to the absence of clamping diodes and capacitors [59]. However, due to usage of an individual DC source for every 1-Φ H-bridge this inverter faces the problem of voltage misbalancing among different phases.

^{0}V

_{dc}, 2

^{1}V

_{dc}… 2

^{n−1}V

_{dc}[62], whereas the trinary asymmetric topologies are selected in the ratio of 3

^{0}V

_{dc}, 3

^{1}V

_{dc}… 3

^{n−1}V

_{dc}[63]. The number of 1-Φ modules required for the generalized m-level binary CHB-GCMLI are (m+8)/9, while trinary CHB-GCMLI required (m/9+3)/2. The input sources are arranged in a trinary manner to achieve 09 level voltages in a topology proposed in [11]. It uses 02 H-bridges, and among them, one of the bridges is being fed into the FC inverter as presented in Figure 6d.

#### 4.4. Modular GCMLI (M-GCMLI)

_{1}and S

_{2}), 01 DC capacitor (C), and 02 reverse diodes. Both the switches of SM cannot be operated at the same time i.e., when S

_{1}is turned ON S

_{2}must be turned OFF and vice versa. Hence, the operation of the SM can be defined for two operation modes. The first operating mode also known as the interleaved state is achieved by turning ON S

_{1}and turning OFF S

_{2.}In the second operating mode, when S

_{1}is turned OFF and S

_{2}is turned ON, the SM is said to be in a bypassed state. Under usual operating situations, the voltage at the terminal of SM can either be 0 or equal to capacitor voltage [65]. Moreover, the fluctuation in the capacitor voltage and inter-phase current circulation will occur in SM if the DC voltage is unstable. Therefore, to make sure the DC voltage stability the arm of the lower bridge is required to be disconnect every time when SM gives an input at the upper arm and vice versa [66].

- Auxiliary Functionalities: The inverter must have the ability to provide the auxiliary functionalities when demanded from the grid operator. Moreover, the voltage compensation mostly focused on voltage interruption, swell, and sag. While the current compensation mostly focused on active and reactive components. However, unbalance and harmonic compensation require further research.
- Efficiency: The selection of a grid-connected PV inverter is mainly based on its efficiency. The inverter must be capable to attain a high efficiency over a wide range of loads. Due to the technological advancement in the last few decades, the power losses of the inverter are greatly reduced, and high efficiency is achieved.
- Anti-Islanding Detection: A GCPVI must have the capability to detect the islanding situation and disconnect it from the grid for safety purposes, while supplying power to the local load. In these conditions, the function of the inverter is usually referred to as anti-islanding.
- Cost: The selection of an inverter mainly depends on the manufacturing and installation cost. There is a tradeoff between the manufacturing cost and the performance and power quality of the inverter. On the contrary, the installation cost mainly depends on land acquisition, labor, and local factors that vary from region to region.
- Leakage Current: In transformer-based inverters the leakage current is interrupted by the galvanic isolation. However, in transformer-less MLIs the leakage current is a major issue as it increases the losses, harmonics in the grid injected current, and electromagnetic interference. Therefore, for a grid-connected system those MLIs are needed to be selected that are capable is to reduce the leakage current according to the international regulations.
- Power Density and Capacity: Generally, most of the experimental prototypes of GCMLIs are of low power density and capacity. Therefore, high power rated prototypes should be focused and enabled their integration with medium and high voltage grid connection.
- DC-Link Capacitor: The DC-link capacitor plays an important role in supplying the AC component of input current the inverter. The control and design of the DC-link capacitor is not an easy task and become more complex if their number rises.
- Switching Frequency: The switching frequency of small capacity GCMLIs is usually higher as compared to the large capacity inverters.
- Semiconductor Devices: The cost of GCPVIs mainly depends on the number and power ratings of the switches. Therefore, those topologies should be focused that have less number of switches with low voltage ratings.
- Galvanic Isolation: It is one of the most important requirements for safety purpose. In transformer-based inverter the galvanic isolation is provided by the transformer. However, in transformer-less inverter topologies, the isolation is achieved by using switches. Hence, the inverter should be selected according to the requirement of galvanic isolation.

## 5. Modulation Techniques for Multi-Level Inverters

#### 5.1. High Switching Frequency (HSF)

#### 5.1.1. PWM

_{r}) with the carrier waveform (V

_{c}). These signals are then fed to the gate of the switches to drive them. The behavior of PWM depends on two components, these are frequency and duty cycle [89]. Moreover, to generate gating signals 02 approaches, i.e., uni-polar and bi-polar approaches are used. To generate 03 voltage levels by using a uni-polar approach, two V

_{r}signals having opposite phases are compared with V

_{c}. While in bipolar, one V

_{r}is compared with V

_{c}to generate 3-levels voltage in a 2-level inverter [90]. Recently, numerous research work is done on PWM schemes and are applied on different GCMLIs for different purposes, such as in 3-level NPC, a PWM scheme is applied to overcome the switching and conduction losses [91]. While a modified PWM scheme is proposed for reduced NPC to increase the level count, improve the output waveforms, and to reduce the inverter cost [92]. A PWM scheme is used to eliminate the harmonic contents for high and low modulation index areas in FC topology [93]. A PWM scheme applied in CHB topology for improving the supply line quality index [94]. Moreover, it is applied in M-MLI to enhance the power factor, reduces the harmonic content and voltage stress on switches, and ensures the fast dynamic response [95]. The PWM techniques are classified into two main types, named as carrier based and reference based PWM.

#### Carrier-Based PWM (MCB)

#### Reference-Based PWM

_{r}) is constantly compared with V

_{c}. The pulse will be generated only if V

_{r}is above the V

_{c}; as a result the corresponding power switch will be turned ON. However, when V

_{r}is below the V

_{c}; then no pulse will be generated, and the switch remained in turned OFF condition [79]. Depending on the structure of MLI, V

_{r}can either be uni-polar or bipolar [97]. The RB-PWM methods are divided into seven different types, named as (a) rapezoidal PWM, (b) sinusoidal PWM (SPWM), (c) staircase modulation, (d) 60° PWM, (e) hybrid reference, (f) third harmonic injection (THI), and (g) discontinuous reference.

_{c}is compared with V

_{r}then this technique is said to be an SPWM [100]. In the staircase technique, the pulses are generated by choosing the step count according to the number of levels required in output waveforms. The selection of a suitable modulation frequency also plays an important role in this technique. However, this method is not recommended to use if the number of pulses in one cycle exceeds 15 [101]. In 60° PWM technique, the top of the pulses are made flat from 60° to 120° in positive and from 240° to 300° in negative half cycles, respectively [102]. This method eliminates the triple harmonics 3-Φ output waveforms and reduces the switching losses. In a hybrid method, two reference signals are combined to make a hybrid reference signal and are used in such a manner that one reference signal is used in the primary half-cycle and the other is used in the second half-cycle. When the selected harmonics are injected to V

_{r}, then the THI reference is formed [103]. The discontinuous reference signals are utilized to adjust the voltage offset and to minimize the switching losses [104].

#### 5.1.2. SVM

#### 5.2. Fundamental Switching Frequency (FSF)

#### 5.2.1. Selective Harmonic Elimination (SHE)

#### 5.2.2. Switching Angle Calculation (SAC)

_{1}). The switching angles in the third (180°–270°) and fourth (270°–360°) quadrants can be calculated as (π + α (n − 1)/2) and (2π − α

_{1}), respectively [117]. The SAC is further classified into feed forward, half equal phase, equal phase, and half height method. The comparative analysis of these four methods for SAC is described in Table 5 [116]. Among these, the feed forward MT is highly recommended for RE applications especially for PV, as it can be applied to any voltage level due to the wide spectrum nature of α and produce the output waveforms having very low THD.

#### 5.2.3. Space Vector Control (SVC)

#### 5.2.4. Nearest Level Control (NLC)

## 6. Controllers Reference Frames

_{S}presents the applied regulator. In case of current regulation, it provides good power flow regulation and harmonic rejection. However, a single sensor is used to protect the inverter from over-current [124]. In case of voltage regulation this control structure does not offer any protection from the short circuit or resonance damping; therefore, an additional prerequisite is needed to improve the system reliability and stability [125].

_{D}

_{1}and H

_{D}

_{2}present the outer and inner regulators respectively. An H

_{D}

_{2}is a fast internal loop that controls the grid injected current. The issues like protection of devices from the current and power quality enhancement are related to the current loop. The H

_{D}

_{1}is a slow external voltage loop that regulates the voltage at the DC-link. The power flow balancing and optimal regulation issues are generally associated with the DC-link external voltage controller [20]. The transfer functions of both loops (outer and inner) are independent from each other; therefore, both the loops can be designed in a decoupled manner. However, for stability purpose, the dynamic speed of an outer loop must be 5–20 times slower than the inner loop [126]. Instead of the cascade of current and voltage control loops, the cascade of power and voltage loops can also be used, and the grid injected current is controlled indirectly.

_{T}

_{1}, H

_{T}

_{2}, and H

_{T}

_{3}are the applied regulators. The implementation and analysis of this structure is more complex than the single or double structures, as every loop bandwidth is limited by the response delay of the inner loop. Therefore, it is very difficult to attain width bandwidths for the most outer loop. Among the control loop structures, a triple loop structure provides more control flexibility and makes it more beneficial for the high performance of the grid-connected inverters.

#### 6.1. dq Reference Frame

_{d}and I

_{q}) and voltage components (V

_{d}and V

_{q}) into dq frame using a Park transformation. It converts the grid voltage and current into a reference system in which they revolve continuously with the grid voltage. By using this approach, the control variables are converted from the sinusoidal domain are transformed into DC domain which can easily be controlled and filtered [129]. In the last few years, numerous controllers are applied in a single loop structure such as proportional-integral (PI) [130], proportional (P) [131], dead-beat (DB) [127], proportional-resonant (PR) [132], in which the PR shows a prominent performance. PI is usually used in dq reference frame in GCPPPs due to its simple configuration, uncomplicated control, and easy filtering. A generalized configuration of proportional integral (PI) applied in dq reference frame to GCPVI is presented in Figure 9a [133]. The current components in a dq reference frame (I

_{d}and I

_{q}) are then compared with the reference current components (I

_{dref}and I

_{qref}). The error generated from the comparison is regulated by the PI regulator and the signal is feed to the PWM modulator to drive the switches of the inverter.

#### 6.2. abc Reference Frame

#### 6.3. αβ Reference Frame

_{a}, I

_{b}, and I

_{c})and voltage (V

_{a}, V

_{b}, and V

_{c}) are converted into current (I

_{α}and I

_{β}) and voltage (V

_{α}and V

_{β}) in αβ frame by using a Clark transformation, respectively. It is used in both 3-Φ systems and sometimes in 1-Φ systems. In recent years numerous triple loop control strategies are developed that are applied in different reference frames such as DB-DB-PI [139], DB-proportional integral derivative(PID)-repetitive filter [140], and hysteresis controllers (HC)-PI-P [141]. A generalized configuration of a triple loop proportional resonant (PR) control strategy applied in a cascaded manner in αβ reference frame is presented in Figure 9c [142]. Three PR controllers are applied in a cascaded manner to measure and regulate the grid injected current, capacitor voltage of an inductive capacitive inductive (LCL) filter, and current of the primary inductor of LCL filter. The control variables are converted into two sinusoidal quantities, which eliminate the steady-state errors and achieve a high gain around resonance frequency (f

_{r}). Therefore, as compared to PI, PR controllers have gained more popularity due to the elimination of steady-state error and fast dynamic response, and they have been reported in different literature that they are related to the current control of power system [143]. However, the hardware implementation of PR in αβ frame is complex and the power factor is also not fully controlled.

## 7. Control Strategies for Grid-Connected PV Systems

#### 7.1. Linear Controllers

#### 7.1.1. Classic Controllers

#### 7.1.2. Proportional Resonant (PR) Controllers

#### 7.1.3. Linear Quadratic Gaussian (LQG) Controllers

#### 7.2. Predictive Controllers (PC)

#### 7.2.1. Deadbeat Controllers

#### 7.2.2. Model Predictive Controller (MPC)

#### 7.3. Robust Controllers

#### 7.3.1. Mu-Synthesis Controllers

#### 7.3.2. H-Infinity Controllers

^{∞}and repetitive controllers to regulate the current of the grid-tied VSIs. Different responses such as steady-state response without local loads, non-linear local loads, and unbalanced resistive loads as well as the dynamic response without loads are also studied and investigated. This approach performs very well in terms of suppression of THD, but the main drawback of this approach is its slow dynamic response. An H

^{∞}controller designed for renewable integration has the potential to attain small tracking errors and have low THD in the grid injected current [158]. To improve the power quality and exchange of grid current the authors in [159] proposed an H

^{∞}repetitive control. It enables the inverter to inject the high-quality current into the grid, even in unbalanced or non-linear local loads. Moreover, this controller also has the capability to switch the inverter operation from grid-connected to stand-alone and vice versa.

#### 7.4. Non-Linear Controllers

#### 7.4.1. Sliding Mode Controllers (SMC)

#### 7.4.2. Partial or Full Feedback Linearization (PFL or FFL) Controllers

#### 7.4.3. Hysteresis Controllers (HC)

#### 7.5. Adaptive Controllers

#### 7.6. Intelligent Controllers

#### 7.6.1. Neural Network (NN) Controllers (NNC)

#### 7.6.2. Repetitive Controllers (RC)

^{−1}) and S(z

^{−1}) present the transfer functions of the controller. The RC shows a very good performance for non-linear periodic load, but the transient response of the controller is not very attractive. To cope with this problem, it can be used (in a cascaded or parallel structure) with the highly transient response controllers, such as hysteresis and deadbeat etc. Therefore, the authors in [185] proposed a PI+RC controller for grid-tied PV inverters. To enhance the adjustment capability and response time of the system a weighting factor m is introduced in the PI branch.

#### 7.6.3. Fuzzy Logic Controllers (FLC)

^{∞}and µ synthesis controllers due to their high capability to handle the system uncertainties. The SMCs show a very reliable performance in GCPVIs because they are highly insensitive to variables variation and disturbances but cause a shattering effect. Therefore, it can be used with other controllers such as fuzzy, direct power control, NN to cope with the chattering effect. Moreover, the HC controller presents a very good performance in fulfilling the grid functionalities but to limit the measured current within its hysteresis band is a major drawback. Hence, a combined approach of HCC and high order SMC can be a feasible solution. The grid functionalities can be enhanced more by using a combination of three different controllers such as a combination of DB, classical controller, and RC can be used to control the grid-tied inverter. Similarly, a combination of adaptive, classical, and intelligent controllers can also be used. As the intelligent controls do not require exact system parameters for operation, the fast transient response of the classical controllers, and the adaptive capability of the adaptive controller make this combination a good choice for grid-connected PV inverters.

## 8. Future Scope of Research

_{2}emissions and other environmental concerns the world has adopted renewable energy resources for energy generation. Among the RES, solar energy is gaining more interest and among the RES its number comes after hydel and wind resource for energy generation. However, due to PV’s intermittent nature its penetration in such a large scale brings some side effects and challenges the security, reliability, and stability of the system. Therefore, for the accurate and robust integration of PV with utility grid the PE inverters to be examined and investigated so that they can meet the requirements specified by the operator and provide a high quality power with very low harmonic contents. In recent years, numerous developments have been made in the designing of highly reliable and efficient inverter topologies for grid-connected systems. A few of the active research topics in this domain are (a) the design of transformer-less inverter topologies that have a simple structure with high structure modularity and attain the high voltage level by using fewer semiconductor switches, and (b) most of the MLI prototypes are of low capacity. Therefore, high power rated prototypes should be focused and enabled their integration with medium and high voltage grid connection (c) a combined approach of modulation techniques and intelligent algorithms (particle swarm optimization (PSO), genetic algorithm (GA), etc.) should be used to provide a high quality inputs to the grid with low harmonic contents, and (d) development of the GCMLIs control strategies that help in providing the intelligent and ancillary services and enhances the power quality and grid reliability.

## 9. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 1.**Total installed capacity of photovoltaic (PV) (2008–2018) [3].

**Figure 3.**Classification of inverters [36].

**Figure 4.**Configuration of grid-connected PV inverters: (

**a**) central; (

**b**) string; (

**c**) multi-string; and (

**d**) AC modules [45].

**Figure 8.**Controller structure: (

**a**) single loop with H

_{S}regulator; (

**b**) double loop with H

_{D}

_{1}and H

_{D}

_{2}are the outer and inner loop regulators respectively; and (

**c**) cascaded pattern of triple-loop.

**Figure 10.**Different types of control strategies [144].

**Figure 11.**Block diagram of controllers (

**a**) proportional resonant (PR) [145]; (

**b**) linear quadratic gaussian (LQG) [146]; (

**c**) predictive controllers (PC) [147]; (

**d**) deadbeat controllers [22]; (

**e**) MPC [149]; (

**f**) robust controllers [153]; (

**g**) hysteresis controllers HC [173], (

**h**) adaptive controllers [175], (

**i**) repetitive controllers (RC) [184]; and (

**j**) fuzzy logic controllers (FLC) [186].

Ref. | GS PV | PV CS | CI | IT | MT | CRF | CT | FS |
---|---|---|---|---|---|---|---|---|

[23] | ✓ | ✗ | ✓ | ✓ | ✗ | ✓ | ✗ | ✓ |

[24] | ✓ | ✗ | ✗ | ✓ | ✗ | ✓ | ✗ | ✗ |

[25] | ✗ | ✗ | ✗ | ✓ | ✓ | ✓ | ✓ | ✗ |

[26] | ✓ | ✗ | ✓ | ✓ | ✗ | ✗ | ✗ | ✓ |

[27] | ✓ | ✗ | ✗ | ✓ | ✗ | ✗ | ✗ | ✓ |

[19] | ✗ | ✗ | ✗ | ✗ | ✓ | ✓ | ✓ | ✗ |

[28] | ✗ | ✓ | ✓ | ✓ | ✗ | ✓ | ✗ | ✓ |

[29] | ✗ | ✗ | ✗ | ✓ | ✓ | ✗ | ✗ | ✗ |

[30] | ✗ | ✗ | ✗ | ✗ | ✗ | ✓ | ✓ | ✗ |

[21] | ✗ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✗ |

[31] | ✓ | ✗ | ✓ | ✓ | ✗ | ✗ | ✓ | ✓ |

[32] | ✗ | ✓ | ✓ | ✓ | ✗ | ✗ | ✗ | ✓ |

[33] | ✗ | ✓ | ✓ | ✓ | ✓ | ✗ | ✗ | ✗ |

[34] | ✓ | ✗ | ✓ | ✗ | ✗ | ✓ | ✓ | ✗ |

[OS] | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |

Performance | Central | String | Multi-String | AC Module |
---|---|---|---|---|

Very High | Variation of DC input voltage | ------ | ------ | Maintenance Installation cost MPPT efficiency Flexibility Reliability |

High | Cables cost Voltage balancing DC power loss Switching loss Panels mismatching Robustness | Installation cost MPPT efficiency Flexibility Reliability | Variation of DC input voltage | AC Cables cost AC Power loss |

Medium | Installation cost | DC Cables cost DC voltage variation AC Power loss Voltage balancing | Maintenance MPPT efficiency Flexibility Reliability Robustness DC and AC power loss Switching loss Installation and cables cost | ------ |

Low | MPPT efficiency Flexibility Reliability Maintenance AC Power loss | Robustness Cables cost DC Power loss Switching loss Panels mismatching | Voltage balancing Panels mismatching | Voltage balancing |

Very low | ------ | ------ | ------ | Robustness Cables cost DC voltage variation DC Power loss Switching loss Panels mismatching |

Power rating | 1–50 MW | 1–5 kW/string | 1–50 kW | 500–600 W |

Cost | Lowest cost | Costly than centralized inverter | Costly than centralized inverter | Highest cost |

Type of GCMLI | Pros | Cons |
---|---|---|

NPC-GCMLI | Simple design Fast dynamic response Low voltage rating switches are needed High efficiency | As level increases the clamping diode count increases As level increases the complexity to balance the DC-link increases DC-link voltage regulation is required |

FC-GCMLI | During power outage it has the capability to provide an extra ride through facility Phase redundant Low component count Low stress on components Low THD and have high modularity | As level increases the capacitor count increases As level increases the control system become more complicated High installation cost Less efficient due to low switching efficiency |

CHB-GCMLI | Provide modular solution to achieve high voltage level Good fault tolerance Highly reliable | The inverter faces the problem of voltage misbalancing among the different phases Separate DC sources are used |

M-GCMLI | Suitable for all voltage levels High modularity Low component count As the level increase the power switches count not increases Simpler structure Low THD and have compact size | High thermal losses High conduction losses High voltage ripples through SMs capacitors Current flows within inverter Large quantity of DC voltage sources (isolated) are required |

**Abbreviations:**THD: Total Harmonic Distortion; SM: Sub-modules; M-GCMLI: Modular Grid-Connected Multilevel Inverter.

Ref. | MLI Topology | NOL | NOP | MT | C | SF (kHz) | CP (kW) |
---|---|---|---|---|---|---|---|

[67] | CHB | 05 | 3-Φ | SV-PWM | PI | 10 | --- |

[68] | M | 7 | 3-Φ | MC-PWM | PI | 10 | 0.4 |

[69] | Reduced switch | 7 | 1-Φ | MC-PWM | --- | --- | --- |

[70] | E-Type | 7 | 3-Φ | PWM | --- | 20 | 4 |

[71] | CHB | 13 | 1-Φ | PWM | --- | 5 | --- |

[72] | Three phase | 5 | 3-Φ | MC-PWM | --- | 20 | 1 |

[73] | Diode Clamped | 5 | 1-Φ | PWM | --- | --- | --- |

[74] | symmetrical | 7 | 3-Φ | PWM | --- | --- | --- |

[75] | Hybrid | 5 | 3-Φ | PWM | Finite Control Set-MPC | 6 | 7.5 |

[76] | NPC Back to Back | --- | 3-Φ | PWM | MPC | 10 | 0.28 |

[77] | CHB | 5 | 1-Φ | LS-PWM | FO-PID | 2 | --- |

[78] | CHB | 7, 15 | 1-Φ | MC-PWM | --- | --- | --- |

[79] | CHB with T type | m | 3-Φ | PS-PWM | PI | 3 | 1 |

[80] | Modular | m | 3-Φ | LS-PWM | PR | 1 | --- |

[81] | CHB | 7, 9 | 1-Φ | LS-PWM | CPT | 12 | 2 |

[82] | Cascaded Full-bridge with FC | 9 | 1-Φ | PWM | Hysteresis | 20 | --- |

[83] | Asymmetrical Cascaded | 17 | 1-Φ | SHE-PWM | --- | --- | --- |

[84] | Quasi Z-Source Based NPC | 5 | 1-Φ | LS-PWM | PI | 10 | 0.5 |

[85] | Modified DC link | 7 | 1-Φ | MC-PWM | --- | 6 | --- |

[86] | NPC | 3 | 3-Φ | SV-PWM | --- | 2 | 1.1 |

**Table 5.**Comparative analysis of different switching angle calculation (SAC) methods [116].

α Calculation Methods | α, for i = 1, 2,…(n − 1)/2 | THD in Output Voltage | Nature of α | Remarks |
---|---|---|---|---|

Feed Forward | sin^{−1}((i − 0.5)/n) | Small | High | Feasible for any voltage level |

Half Equal Phase | 180°/(n + 1) | High | Low | Feasible for low voltage level |

Equal Phase | 180°/n | High | Very Low | Feasible for low voltage level |

Half Height | sin^{−1}((2i − 1)/(n − 1)) | Medium | Moderate | Feasible for medium and low voltage levels |

Ref. | NOP, CRF | CC | DLC | FL | CP | F | MT | A |
---|---|---|---|---|---|---|---|---|

[133] | 3-Φ, (dq) | MPC | --- | S-L | C | L | SVM | PV |

[139] | 3-Φ, (abc) | DB, PI | DB | M-L | C, V | LCL | DPWM | G |

[152] | 1-Φ | FSC-MPC | --- | S-L | C | L | PWM | G |

[154] | 3-Φ, (dq) | μ-synthesis | PI | M-L | C, V | LC | PWM | PV |

[158] | 3-Φ, (dq) | H-infinity | PI | M-L | C, V | LC | PWM | RE |

[137] | 3-Φ, (dq) | SMC | --- | S-L | C | L | PWM | PV |

[162] | 3-Φ, (αβ) | SMC-DPC | SMC-DPC | M-L | V, P | L | SVPWM | PV |

[166] | 3-Φ, (dq) | FFL | LC | M-L | C, V | L | SVPWM | PV |

[168] | 1-Φ | PFL | PFL | M-L | V, C | L | PWM | PV |

[181] | 3-Φ, (abc) | Fuzzy Neural Network | Fuzzy Neural Network | M-L | V, P | L | PWM | PV |

[182] | 3-Φ, (dq) | ANFISPID | ANFISPID | M-L | V, C | L | PWM | PV |

[184] | 3-Φ, (dq) | Repetitive | --- | S-L | C | L | SVM | PV |

[192] | 3-Φ, (dq) | PI | PI | M-L | V, C | LC | SVM | DG |

[193] | 3-Φ, (dq) | Instantaneous Active Reactive Control | PI, PR | M-L | V, P | L | PWM | G |

[194] | 3-Φ, (dq) | PI | PI | M-L | V, C | L | PWM | DG |

[195] | 3-Φ, (αβ) | I | --- | S-L | C | L | PWM | DG |

[196] | 3-Φ, (dq) | Reactive Power Control | PI | M-L | V, P | LC | PWM | PV |

[197] | 1-Φ | PR | PI | M-L | V, C | LCL | PWM | G |

[198] | 1-Φ | PI, PR | --- | S-L | C | LCL | SPWM | G |

[199] | 1-Φ | PI, Hysteresis | PI | M-L | V, C | LC | PWM | G |

[200] | 3-Φ, (αβ) | PR | PI | M-L | V, P | LCL | PWM | DG |

[201] | 1-Φ | --- | Adaptive droop | M-L | V | LCL | PWM | G |

[202] | 3-Φ, (dq) | Adaptive | PI | M-L | V, C | LC | SVPWM | DG |

[203] | 3-Φ, (αβ) | MPC | --- | S-L | V, C | L | PWM | PV |

[204] | 3-Φ, (αβ) | Hysteresis MPC | --- | S-L | C | LCL | PWM | G |

[205] | 3-Φ, (αβ) | Predictive DPC | PI | M-L | V, P | L | PWM | PV |

[206] | 3-Φ, (αβ) | MPC | --- | S-L | C | LCL | PWM | G |

[207] | 3-Φ, (αβ) | Fuzzy | PI | M-L | V, C | L | SVPWM | PV |

[208] | 1-Φ | Fractional order PR | --- | M-L | C, P | L | SPWM | PV |

[209] | 3-Φ, (dq) | Fractional order PI | Fractional order PI | M-L | V, C | LCL | PWM | PV |

[210] | 3-Φ, (dq) | PI | PI | M-L | V, C | LCL | PWM | PV |

[211] | 3-Φ, (dq) | PR | PI | M-L | V, C | LCL | PWM | PV |

[212] | 1-Φ | Fuzzy SMC | --- | S-L | V | L | PWM | PV |

[213] | 3-Φ, (dq) | Droop | --- | M-L | V, C | LC | PWM | DG |

[214] | 3-Φ, (dq) | PI | PI | M-L | V, C | L | PWM | PV |

[215] | 3-Φ, (dq) | PI | PI | M-L | V, C | L | SPWM | PV |

[216] | 3-Φ, (dq) | PI | PI | M-L | V, C | L | SVPWM | PV |

[217] | 1-Φ | PI, MPC | PI, MPC | M-L | V, C | L | PWM | PV |

[218] | 3-Φ, (dq) | PI, Vector control | PI | M-L | V, C | L | PWM | PV |

[219] | 3-Φ, (dq) | Fractional order SMC | --- | S-L | C | L | PWM | PV |

[220] | 3-Φ, (dq) | Voltage look-up table method | Voltage look-up table method | M-L | V, C | L | VLUT | DG |

[221] | 3-Φ, (αβ) | H-infinity | --- | S-L | C | LCL | SVM | G |

[222] | 3-Φ, (αβ) | MPC | --- | S-L | C | LCL | PWM | G |

[223] | 1-Φ | Fractional order RC | --- | S-L | C | LCL | PWM | G |

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**MDPI and ACS Style**

Ali Khan, M.Y.; Liu, H.; Yang, Z.; Yuan, X.
A Comprehensive Review on Grid Connected Photovoltaic Inverters, Their Modulation Techniques, and Control Strategies. *Energies* **2020**, *13*, 4185.
https://doi.org/10.3390/en13164185

**AMA Style**

Ali Khan MY, Liu H, Yang Z, Yuan X.
A Comprehensive Review on Grid Connected Photovoltaic Inverters, Their Modulation Techniques, and Control Strategies. *Energies*. 2020; 13(16):4185.
https://doi.org/10.3390/en13164185

**Chicago/Turabian Style**

Ali Khan, Muhammad Yasir, Haoming Liu, Zhihao Yang, and Xiaoling Yuan.
2020. "A Comprehensive Review on Grid Connected Photovoltaic Inverters, Their Modulation Techniques, and Control Strategies" *Energies* 13, no. 16: 4185.
https://doi.org/10.3390/en13164185