An Embedded Communication Method for In-Home Energy Routers With Power/Signal Dual Modulation

This article proposes a novel embedded communication strategy for in-home energy routers (IHERs). It is based on the power/signal dual modulation (PSDM) principle and applied in the small-scale community energy local area network (E-LAN). The proposed communication strategy multiplexes power converters as data transmitters, and thus high cooperation and synchronization between power flow and information flow are achieved. In addition, system reliability is enhanced since communication module has practically the same reliability as the power module. A typical IHER’s structure and operation principles are presented, based on which the detailed design of embedded communication is proposed. For distributed power management of community E-LAN, both intra-IHER communication and inter-IHERs communication are involved, and their channels are modeled mathematically. IHER interconnection interface converters (IICs) play a significant role in power exchange between IHERs, and their operation modes are analyzed in detail. Finally, an experimental prototype is built to validate the feasibility of the proposed method.


23
T HE need to diversify away from fossil fuel generation 24 due to concerns over energy security, fuel price volatil-25 ity, and the climate challenge is driving the deployment of 26 nonconventional renewable energy (wind, small hydro, solar, 27 tidal, geothermal, and in some cases waste) [1]. Because of 28 their distributed, intermittent, and fluctuated characteristics, 29 energy management is considered a key paradigm for the 30 realization of complex energy systems [2]- [4], and distributed 31 power management and flexible bidirectional power flow con-32 trol are required. The energy Internet (EI) concept has been 33 proposed [5]-[7] as a feasible solution, which deeply integrates 34 energy technology and information technology, presenting a 35 green vision of evolution [8]- [10]. 36 Currently, EI has received extensive attention and several 37 structures have been proposed [11]. Generally, there are three 38 mainstream structures, which are bus structure, tree structure, 39 and mesh structure [12]. Bus structure has great advantages 40 of extension, but the common bus encounters congestion 41 challenges in condition of large-scaled power and informa-42 tion interaction. Tree structure can efficiently isolate faults; 43 however, it faces the bottleneck of efficient power control 44 and management in promotion. Mesh structure does not need 45 a central controller and gives more autonomy to energy 46 entities, achieving better robustness and fault tolerance [13]. 47 It requires high cooperation and synchronization between the 48 power module and the communication module to guarantee 49 distributed, reliable, and flexible power management, and it 50 is usually applied in small-scale energy local area network 51 (E-LAN), such as a residential community energy network. 52 In a community E-LAN, the in-home energy router (IHER) 53 plays a significant role as the key element, interconnection 54 equipment, and power management units [14] for each house. 55 Meshed connections require proper energy routing to achieve 56 efficient and intelligent distributed power management, for 57 which real-time and reliable communication between IHERs 58 are indispensable. Conventional communication approaches 59 mainly include wireless communication, fieldbus, and Ether-60 net. Wireless communication technology is commonly used, 61 which mainly includes ZigBee, Bluetooth, and Wi-Fi [15]. 62 It has the advantages of low cost and simple structure, but 63 2168-6777 © 2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See https://www.ieee.org/publications/rights/index.html for more information. This article is arranged as follows: Section II provides 147 the general structure and operation principle of the IHER. 148 Section III presents the principle and design details of PSDM 149 method for IHER application, including intra-IHER com-150 munication design and inter-IHERs communication design. 151 In Section IV, experimental validation is given based on a 152 prototype system. Finally, a conclusion is drawn in Section V. 153

154
OPERATION PRINCIPLE OF IICS 155 Fig. 1(a) shows a typical structure of an IHER, which 156 includes three modules: power module, communication mod-157 ule, and control module. The power module is composed of a 158 common dc power bus and several interface converters (ICs) 159 connected in parallel. In this article, a 370-V dc power bus is 160 adopted, and the ICs are divided into three categories: 1) dc 161 48-V ICs, which are compatible with an LED lighting system 162 and chargers for consumer electronics; 2) dc 400-V ICs, which 163 are compatible with PV power generations and electric vehicle 164 chargers; and 3) ac 220-V ICs, which are compatible with 165 the main grid and some household appliances, like washing 166 machines and refrigerators. To enhance the universality, all 167 ICs are designed to be bidirectional, and bridge topologies are 168 employed for the convenience of IC reconstruction and mul-169 tiplexing in future research. Therefore, two-stage Buck/Boost 170 converters are adopted as dc 48-V ICs; Buck/Boost converters 171 are adopted as dc 400-V ICs; full bridge converters are adopted 172 as ac 220-V ICs. The control module is composed of several 173 controllers corresponding to each IC. The communication 174 module is composed of data transmitters and communication 175 wires, responsible for the exchange of power state and control 176 information between IHERs.    In this article, by employing PSDM, all the ICs are multi-195 plexed as data transmitters, which means no separate commu-196 nication module is required, while the communication function 197 will be embedded into power and control modules, as shown 198 in Fig. 1(b). All the ICs are responsible for both power 199 conversion and data modulation, whereas all the common dc 200 buses in IHERs and power links between IHERs will transmit 201 both power and information. Using the proposed PSDM method, power conversion and 208 data modulation can be achieved simultaneously without addi-209 tional hardware circuits.  Data are directly modulated to the additional sinusoidal 221 carrier, and amplitude shift keying (ASK), frequency shift 222 keying (FSK), and phase shift keying (PSK) are the three 223 mainstream digital data modulation approaches. ASK modula-224 tion is sensitive to noises, especially in multi-ary modulations, 225 thus not suitable in the power converter system with much 226 more serious noise interferences than dedicated communica-227 tion systems. FSK modulation encounters the challenge of 228 crosstalk in transmission, and its bandwidth utilization is 229 relatively low. PSK modulation has the best noise immunity, 230 and the bandwidth utilization is high, especially in multi-ary 231 modulation conditions.  signal is then sent to the digital processor for demodulation.

263
In this article, the FFT algorithm is adopted to calculate the 264 corresponding phase and amplitude of the received signals. In multi-machine conditions, several information flows may 268 cause crosstalk to deteriorate the communication reliabil-269 ity. To solve this problem, the frequency division multiple 270 access (FDMA) strategy is adopted, and each power converter 271 accessing to the same common transmission line is allocated 272 with unique and orthogonal frequency.

273
The frequency selection of injected carrier is another key 274 issue in PSDM. Taking the PI voltage-controlled Buck/Boost 275 converter (operating in Buck mode) as an example for quanti-276 tative analysis, the system diagram is shown in Fig. 5, and the 277 transfer function from the voltage reference V ref to the output 278 voltage V o is derived as follows: (2) 280 In a typical Buck/Boost converter, (1) can be derived as 281 follows: where R 1 and R 2 are sampling resistances, V o is the output 284 voltage, D is the duty cycle, V M is the peak voltage of the 285 PWM carrier, and K p and K i are proportional and integral 286 parameters in PI control.

287
With typical values adopted (L = 300 μH, C = 330 μF, 288 K p = 0.48, and K i = 480), the system Bode diagram is shown 289 in Fig. 6, and the PI control loop bandwidth is 100 Hz. Band 290 A is within the control loop bandwidth and closed loop data 291 signal control can be achieved, but the communication rate is 292    Fig. 7(a). In this model, voltage-controlled converter 313 (converter 1) equals a voltage signal source v 1 when it 314 sends data, as shown in Fig. 8(a). Correspondingly, current-315 controlled converters (converter 2 to converter n) equal current 316 signal sources i 2 to i n when they send data, as shown in Fig.   317 8(b). When an IC receives data, it equals impedance Z _sin , 318 which is its input impedance from the bus side in carrier 319 frequency, as shown in Fig. 8(c).

320
When the voltage-controlled IC sends data, the voltage 321 carrier is superimposed on the common dc bus, which is Similarly, when a current-controlled IC #m [m is an integer, 324 and 2 ≤ m ≤ n)] sends data, the current carrier is superim-325 posed on the common dc bus, which is depicted as According to the model, the admittance of the common power 328 bus is Based on (5) and (6), the voltage of the carrier can be easily 331 derived.

332
Inter-IHERs communication achieves bidirectional commu-333 nication between neighbor IICs. In the E-LAN, energy routers 334 are connected peer-to-peer via IICs into a mesh structure. 335 Each power link is multiplexed as communication channel 336 connecting neighbor IICs, and the equivalent channel model 337 is shown in Fig. 7(b).

338
In this model, two neighbor IICs are defined as source IIC 339 (voltage-controlled) and load IIC (current-controlled), respec-340 tively, according to the power flow direction. IIC equivalent 341 circuit is the same as intra-IHER communication condition. 342 Since the transmission distance between energy routers is 343 nonignorable, power link impedance is considered in this case. 344 Therefore, when the data are sent by source IIC converter, the 345 carrier is superimposed on its output voltage (power link side 346 voltage), which is The voltage at load IIC (data receiver) is When messages are sent by load IIC, the carrier is super-351 imposed on its input current (power link side current), which 352 is (9) 354 The voltage at source IIC (data receiver) is 355 v RX = i _sin(R_sin + j X_sin).

357
In this article, all ICs adopt bridge topologies, and for IICs, 358 two options are presented for different application require-359 ments, which are Buck/Boost and DAB, respectively.

2) Dual Active Bridge (DAB) IIC:
In DAB IIC, a high-407 frequency transformer T r is employed to achieve desired 408 voltage gain and galvanic isolation.

409
The interconnection structure of neighbor IIC adopting DAB 410 converters is shown in Fig. 10. By controlling the intra-411 bridge and inter-bridge phase shift of DAB, power flow can 412 be controlled flexibly [30], [31]. The four operation modes can be flexibly switched accord-439 ing to different conditions.

440
The DAB IIC converter provides galvanic isolation and the 441 power link voltage is much lower in mode 3 than Buck/Boost 442 IIC, but more complex structure and control algorithm increase 443 the cost and deteriorate the reliability.   Buck/Boost converter is adopted as IIC. Fig. 13 shows the 473 simulation result. It can be seen that a low-frequency sinu-474 soidal carrier adopting 2PSK data modulation is superimposed 475 to the dc power flow.

476
When two or more ICs send data simultaneously, the FDMA 477 strategy is adopted. Fig. 14   are orthogonal in the sampling window, and thus crosstalk is 481 avoided in the FFT demodulation process.

485
In the first condition, Buck/Boost IICs are adopted, 486 as shown in Fig. 9    The third case corresponds to the situation of data exchange 508 without power transmissions. Fig. 17 shows the communica-509 tion initial state establishment and data transmission processes.   To date, communication handshake has been completed and 519 communication initial state has been established. The detailed 520 data transmission process is shown in the zoomed-in views.  is carried out from t 1 , as shown in Fig. 18. 526 In the E-LAN, transmission distance between energy routers 527 is nonignorable. As a result, in the experiment, we increase 528 the distance between IHER #1 and IHER #2 to 100 m, and the 529 BER is measured as 1.3%. The BER is mainly caused by the  Fig. 19. After communication, 550-W power begins 545 transmission at t 3 .To release power transmission, communi-546 cation is firstly carried out at t 1 , as shown in Fig. 20, and 547 then transmission power falls to zero. For 100-m transmission 548 distance condition, the BER is measured as 1%, which is 549 acceptable with proper communication protocols. 550 These experiments have validated the basic functions of the 551 proposed power/data integrated IHER with Buck/Boost IICs 552 and DAB IICs, respectively. It has been validated that four 553 operation modes can be switched flexibly, and some typical 554 situations and processes are focused on, including information 555 exchange with and without power transmissions and power 556 transmission establishment and release.

558
This article proposes an embedded communication method 559 based on the PSDM method for IHERs in meshed E-LAN. The 560 sinusoidal carrier is injected into the control signal, and high 561 cooperation and integration of power control and data modu-562 lation are achieved, ensuring synchronization between power 563 flow and information flow. In addition, the communication 564 is achieved without extra hardware circuits or wires, which 565 enhances the system reliability, and decreases the system cost 566 and complexity compared with other communication methods. 567 In the meshed E-LAN, the proposed communication method 568 is employed in all ICs in each energy router, and intra-569 IHER communication and inter-IHERs communication are 570 achieved, which provide physical basis for distributed power 571 management. A prototype experimental system is constructed 572 and a series of experimental results are obtained, so the 573 effectiveness of the proposed method is verified.

574
There is still some research to be conducted in the future. 575 First, the data modulation method can be optimized, introduc-576 ing improved modulation methods like quadrature amplitude 577 modulation (QAM) and orthogonal frequency division multi-578 plexing (OFDM) to increase the frequency band utilization. 579 Second, all the ICs adopt bridge structures, and hardware 580 multiplexing could be explored to improve the hardware 581 utilization in future research.