# A Unified Topology for the Integration of Electric Vehicle, Renewable Energy Source, and Active Filtering for the Power Quality Improvement of the Electrical Power Grid: An Experimental Validation

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Structure of the Proposed Unified Topology

## 3. Control Algorithms for the Unified Topology

_{g{a,b,c}}) in each of the phases and independently of the reference (i

_{g{a,b,c}}*). Moreover, it should be noted that different references can be used for each phase and the current control must be able to follow such references. The variable v

_{UT{a,b,c}}is the one that is compared with the pulse-width modulation (PWM) carrier to obtain the control signals for the IGBTs of each phase. Distinct PWM carriers are used to guarantee the interleaved operation. As the AC-side interface is based on an interleaved structure per phase, then it is necessary to individually control the current in each leg of each phase. Clearly, each v

_{UT{a,b,c}}variable is compared with the respective PWM carrier. The reference of current for each leg of a given phase must be the same to guarantee the correct interleaved operation, only differing the PWM carrier. Otherwise, the ripple of the resulting current in each phase is not properly minimized (e.g., when the duty-cycle is 50%, the current ripple is necessarily canceled on the resultant current). When the unified topology operates only with active power, the amplitude of the AC currents is directly related to the operating power on the DC-side and must be in phase or in phase opposition with the fundamental component of each voltage. Therefore, a relationship between the currents, voltages and operation power must be established, resulting in a reference of current for each phase (i

_{g{a,b,c}}*) according to:

_{EV}corresponds to the instantaneous operating power of the EV, p

_{RES}corresponds to the instantaneous operating power of the RES, and V

_{g}

_{{a,b,c}}and v

_{g{a,b,c}}correspond, respectively, to the root mean square (RMS) value and to the instantaneous value of the power grid voltages of each phase. Based on the position of the current sensor on the EV interface, the value of p

_{EV}will assume positive or negative values, then the references of current (i

_{g{a,b,c}}*) will be in phase or phase opposition with the voltages. Consequently, since each phase operates in interleaved mode, the reference of current for each leg of each phase (i

_{g{a,b,c}{}

_{1,2}}*) is defined according to:

_{g{a,b,c}}*) must be defined by also considering such possibility (i.e., non-sinusoidal references), and not influencing the control defined by Equation (1), which permits to control the AC-side currents individually and independently of the waveform and frequency. More specifically, for producing reactive power, a signal in quadrature must be considered, which can be obtained from the PLL. The value of reactive power, as well as the period for the unified topology operating in such mode, must be provided by the smart grid. Nonetheless, it is essential to mention that the focus of this paper is to introduce the unified topology and its control, not the smart grid management strategy in terms of defining the reference of reactive power for the unified topology. Therefore, the scope of this paper only has proven the operation of the unified topology considering exemplificative scenarios of a smart grid contextualization. By assuming such considerations, the references of current (i

_{g{a,b,c}}*) are defined by three distinct parts, related with the bidirectional operation with active power (as previously demonstrated by Equation (1)), the operation with reactive power, and the operation with harmonic currents. Thus, the digital implementation of the equation that defines the references of current for each phase of the unified topology is given by:

_{g_cos{a,b,c}}corresponds to the quadrature signals obtained from the PLL, Q* corresponds to the value of reactive power that the unified topology must produce per phase, i

_{gh}[k] corresponds to the harmonic order (which is taken from a PLL), and h corresponds to the amplitude of the harmonic that must be produced. This is the global equation that must be used to control the AC-side currents, but, obviously, depending on the assumed values on the DC-side and the values of the reference for the reactive power and for the harmonics, other equations are derived.

_{UTEV}and v

_{UTRES}are compared with the respective PWM carriers. Since the unified topology has a midpoint on the DC-link, the operation with different voltage levels is possible, depending on whether the voltage on the technology side is less than, equal to, or greater than half the voltage on the DC-link. This feature is very important, as it ensures that each of the IGBTs only operate with half of the voltage of the DC-link, regardless of voltage and current levels on the interfaces of EV or RES, as well as the mode of operation.

_{UTEV}is compared with the respective PWM carrier. The operation principle is the same as previously presented, only differing the direction of the power flow. For each operating mode, the reference of current is defined by the state of the EV, i.e., it is established by the internal control system of the EV, as well as the maximum power that can be extracted from the RES.

## 4. Unified Topology: Computer Simulation and Experimental Validation

_{ga}, v

_{gb}, v

_{gc}) and currents (i

_{ga}, i

_{gb}, i

_{gc}) on the power grid, the currents at the AC-side of the unified topology (i

_{Uta}, i

_{Utb}, i

_{Utc}), the voltages on the DC-link (v

_{dc}

_{1}, v

_{dc}

_{2}), the currents on the DC-side of the unified topology, namely the current on the EV interface (i

_{EV}), and the current on the RES interface (i

_{RES}). During case 1, only the RES is producing power, while the EV is turned off. In this case, all the produced power is clearly injected into the power grid, characterized by balanced and sinusoidal currents in opposition to the voltages. On the other hand, during case 2, the EV starts the charging operation, which is characterized by the increasing power consumption from the power grid, since the power production from the RES is not enough to supply all the power required by the EV charging. Therefore, this case reports a situation of EV charging with power both from the power grid and from the RES. As it can be observed, the operating currents on the AC-side of the unified topology (i

_{UTa}, i

_{UTb}, i

_{UTc}) are balanced and sinusoidal, but, since it is absorbed power from the grid, in case 2, the currents are in phase with the voltages. From the power grid point of view, case 2 (absorbing power) is quite different from case 1 (injecting power). As expected, the DC-link voltages are controlled based on the established reference situation that is independent of the operating case. Consequently, in case 3, the AC-side of the unified topology starts to compensate for the power quality problems introduced by the loads that are connected at the same point of connection to the power grid. In this case, in the sequence of the previous cases (the EV and the RES maintain the same operation as in case 2), no additional active power is exchanged with the power grid, but the AC-side of the unified topology stops operating with sinusoidal currents, while the DC-side of the unified topology maintains the same operation (meaning that the EV charging power is the same and the power produced by the RES is also the same as reported in case 2). In this way, the control algorithm for the AC-side only changes to ensure that the currents of the unified topology (i

_{UTa}, i

_{UTb}, i

_{UTc}) are distorted to compensate for the harmonic distortion caused by the loads connected in the same installation. As consequence, sinusoidal and balanced currents on the power grid side (i

_{ga}, i

_{gb}, i

_{gc}) are obtained. This result shows, in a global way, the principle of operation of the entire unified topology, highlighting the main functionalities when analyzed in terms of controllability. The unified topology start operating sequentially until the limit case in which all the possibilities are operating at the same time and complying with the full functionality. Clearly, as previously mentioned, the sequence of operation can be modified according to the different possible cases since this result is only intended to assess a concrete example.

_{UTa}), as well as the currents (i

_{UTa}, i

_{UTb}) on each leg of this phase. Since these currents are presented in detail, the interleaved operation is highly visible, characterized by the currents i

_{UTa}and i

_{UTb}in phase opposition, and by the current i

_{UT}that is the sum of the currents i

_{UTa}and i

_{UTb}. Consequently, the current i

_{UTa}presents a ripple with a frequency that is the double of the switching frequency (i.e., the double of the ripple frequency of the currents i

_{UTa}, i

_{UTb}). Figure 6 shows the power grid phase-to-phase voltages (v

_{gab}, v

_{gcb}, v

_{gca}) and the voltages of the unified topology on both AC-side (v

_{a}

_{1b1}, v

_{c}

_{1b1}, v

_{c}

_{1a1}) and DC-side (v

_{d}

_{1d2}, v

_{e}

_{1e2}). The voltages on the AC-side (v

_{a}

_{1b1}, v

_{c}

_{1b1}, v

_{c}

_{1a1}) assume the possible three voltage levels (+v

_{dc}, 0, −v

_{dc}), are balanced and are in phase with the respective phase-to-phase voltage (v

_{gab}, v

_{gcb}, v

_{gca}). On the other hand, the voltages on the DC-side (v

_{d}

_{1d2}, v

_{e}

_{1e2}) assume the three voltage levels. In the case of the interface of the EV, in this specific case, it is shown that the voltage assumes the values of 0 and v

_{dc}/2, while in the case of the interface of the RES, in this specific case, it is shown that the voltage assumes the values of v

_{dc}/2 and v

_{dc}. The assumed values on each DC-side can be different, depending on the voltage on the DC interfaces as well as the voltages on the DC-link.

_{d}

_{1d2}measure in the points d

_{1}and d

_{2}represented in Figure 2). A particular case occurs when the voltage of the EV interface is equal to half of the DC-link voltage, resulting in a current with a null-ripple. In this case, it is necessary to control the DC-link to guarantee that both voltages are balanced. In this sense, Figure 10b shows the same variables, as well as the gate-emitter voltages of the IGBTs S

_{13}and S

_{16}, to verify the relationship of the variation between the IGBTs duty-cycle with the voltage of the unified topology (v

_{d}

_{1d2}) and with the EV current (i

_{EV}).

_{17}and S

_{18}. Analyzing the gate-emitter voltages, it is possible to verify that they are controlled in phase opposition aiming to guarantee the interleaved mode also on the RES interface. Additionally, as the voltage in the RES interface (voltage v

_{e}

_{1e2}measure in the points e

_{1}and e

_{2}represented in Figure 2) is higher than half of the DC-link voltage, the voltage of the unified topology changing between two levels, namely half of the DC-link voltage and the full DC-link voltage, is presented. Similar to the EV interface, it is possible to eliminate the current ripple when the voltage of the RES is equal to half of the DC-link. Figure 11b demonstrates the relationship between the current on the RES interface and the gate-emitter voltage of the IGBTs S

_{17}and S

_{18}.

## 5. Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Contextualization of the proposed unified topology connected to the smart grid: (

**a**) Interfacing the EV and the RES with the power grid (with or without active power filtering); (

**b**) Interfacing only the EV with the RES; (

**c**) Interfacing only the EV with the power grid (with or without active power filtering); (

**d**) Interfacing only the RES with the power grid (with or without active power filtering); (

**e**) Interfacing only the power grid with active power filtering.

**Figure 2.**Proposed unified topology for the integration of electric vehicle, RES, and active power filtering for the power grid.

**Figure 4.**Dynamic operation of the unified topology considering the operation of the EV during the charging process, the operation of the RES injecting power to the power grid, or to charge the EV, together with the active filtering for the power grid.

**Figure 5.**Detail of the interleaved operation in phase a, showing the phase current (i

_{UTa}), and the currents (i

_{UTa}, i

_{UTb}) on each leg of phase a, permitting to visualize that the currents i

_{UTa}and i

_{UTb}are in phase opposition, and that the current i

_{UT}is the sum of the currents i

_{UTa}and i

_{UTb}.

**Figure 6.**Detail of the power grid phase-to-phase voltages (v

_{gab}, v

_{gcb}, v

_{gca}) and the voltages of the unified topology on both AC-side (v

_{a}

_{1b1}, v

_{c}

_{1b1}, v

_{c}

_{1a1}) and DC-side (v

_{d}

_{1d2}, v

_{e}

_{1e2}).

**Figure 8.**Experimental validation showing: (

**a**) The voltages on the AC-side (v

_{ga}, v

_{gb}, v

_{gc}); (

**b**) The currents on the AC-side (i

_{UTa}, i

_{UTb}, i

_{UTc}); (

**c**) The harmonic spectrum and the THD value of the voltages on the AC-side; (

**d**) The harmonic spectrum and the THD value of the currents on the AC-side.

**Figure 9.**Experimental validation showing: (

**a**) The currents of the AC-side interface before and after the controlled operation (i

_{UTa}, i

_{UTb}, i

_{UTc}); (

**b**) The currents of the AC-side interface in steady-state (i

_{UTa}, i

_{UTb}, i

_{UTc}); (

**c**) The currents of the AC-side interface (i

_{UTa}, i

_{UTa}

_{1}, i

_{UTa}

_{2}), for phase a, demonstrating the interleaved operation.

**Figure 10.**Experimental validation regarding the EV interface with the possibility to operate with three voltage levels, showing the EV current (i

_{EV}), the voltage of the unified topology (v

_{d}

_{1d2}) on the DC-side interface with the EV, and the gate-emitter voltages of the IGBTs S

_{13}and S

_{16}(v

_{S}

_{13}, v

_{S}

_{16}): (

**a**) EV current and converter voltage; (

**b**) EV current and converter voltage, and the gate-emitter voltages of the IGBTs S

_{13}and S

_{16}.

**Figure 11.**Experimental validation regarding the RES interface with the possibility to operate with three voltage levels, showing the RES current (i

_{RES}), the voltage of the unified topology (v

_{e}

_{1e2}) on the DC-side interface with the RES, and the gate-emitter voltage applied to the IGBTs S

_{17}and S

_{18}(v

_{geS}

_{17}, v

_{geS}

_{18}) to visualize the interleaved operation: (

**a**) RES current, converter voltage, and the gate-emitter voltages of the IGBTs S

_{17}and S

_{18}; (

**b**) Detail of the RES current and the gate-emitter voltages of the IGBTs S

_{17}and S

_{18}.

**Figure 12.**Experimental validation showing a result that validates the operation of the unified topology injecting third order harmonic currents (i

_{UTa}, i

_{UTb}, i

_{UTc}), to compensate these harmonic currents in the power grid: (

**a**) current waveforms; (

**b**) harmonic spectrum.

**Figure 13.**Experimental validation showing a result that validates the operation of the unified topology, compensating almost all harmonic currents ((

**a**) before and (

**b**) after compensation) to contribute to compensate power quality problems on the power grid side: Power grid voltages (v

_{ga}, v

_{gb}, v

_{gc}) and currents (i

_{ga}, i

_{gb}, i

_{gc}).

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**MDPI and ACS Style**

Monteiro, V.; Afonso, J.L.
A Unified Topology for the Integration of Electric Vehicle, Renewable Energy Source, and Active Filtering for the Power Quality Improvement of the Electrical Power Grid: An Experimental Validation. *Electronics* **2022**, *11*, 429.
https://doi.org/10.3390/electronics11030429

**AMA Style**

Monteiro V, Afonso JL.
A Unified Topology for the Integration of Electric Vehicle, Renewable Energy Source, and Active Filtering for the Power Quality Improvement of the Electrical Power Grid: An Experimental Validation. *Electronics*. 2022; 11(3):429.
https://doi.org/10.3390/electronics11030429

**Chicago/Turabian Style**

Monteiro, Vitor, and Joao L. Afonso.
2022. "A Unified Topology for the Integration of Electric Vehicle, Renewable Energy Source, and Active Filtering for the Power Quality Improvement of the Electrical Power Grid: An Experimental Validation" *Electronics* 11, no. 3: 429.
https://doi.org/10.3390/electronics11030429