*Article* **New DC Grid Power Line Communication Technology Used in Networked LED Driver**

#### **Huipin Lin 1, Jin Hu 2, Xiao Zhou 1, Zhengyu Lu <sup>1</sup> and Lujun Wang 3,\***


Received: 9 November 2018; Accepted: 15 December 2018; Published: 18 December 2018

**Abstract:** In order to reduce the cost and improve the reliability, real-time performance, and installation convenience of remote-controlled light-emitting diode (LED) lighting systems, a networked LED driving technology based on the direct current (DC) grid power line carrier is proposed. In this system, an alternating current (AC)/DC bus converter converts the mains into a DC bus with multiple distributed LED drive powers on the DC bus. The AC/DC bus converter receives the user's control command and modulates it into the DC bus voltage. The DC bus waveform changes to a square wave containing the high and low changes of the address information and command information. The LED drive power of the corresponding address receives energy from the DC bus and demodulates the commands, such as turning the lights on and off, dimming, etc., and performs the action. In order to make the waveform of the AC/DC bus converter have better rising and falling edge, this paper adopts the half-bridge topology with variable modal control. In the modulation process, the circuit works in buck mode and boost mode. Distributed LED drivers have DC/DC circuits and very simple demodulation circuits that dissipate energy and information from the DC bus. Through experiments, the technology not only simplifies the use of communication technology in application, but also reduces the application difficulty.

**Keywords:** PLC; bus converter; DC bus; LED driver

#### **1. Introduction**

With the rapid development of light-emitting diode (LED) technology, it is widely predicted that LED will become a new generation of lighting sources. Smart network control is a hot research topic in the field of LED lighting applications. In this application, multiple LED devices generally form an intelligent lighting system through a network, and the LED devices can usually be remotely controlled. In addition to road lighting for large-scale applications [1–4], most of these smart LED lighting systems are often used indoors or outdoors, and the scale is small [5–7].

Figure 1 shows a case for a small-scale LED smart lighting system, such as for commercial lighting, home lighting, landscape lighting, wall washers, high pole lights, etc. In these applications, the number of lamps is small, the distance between two adjacent LED light sources is relatively close, and a computer is typically used to remotely control turning on, turning off, and dimming the lights.

**Figure 1.** Common small networked control light-emitting diode (LED) smart lighting system.

In this small LED smart lighting system, communication between LED drivers is necessary to achieve control. Which communication technology is used determines the real-time performance and reliability of control in the system, while at the same time it also affects the cost, installation, and maintenance. Figure 2 shows descriptions of several common traditional lighting system communication schemes and their characteristics. These small LED lighting systems require a lower-cost solution, however, for 0–10 V, pulse-width modulation (PWM) control, digital addressable lighting interface (DALI) [8–14] and other remote-control schemes, and additional communication lines must be laid, which is unfavorable for installation and maintenance and costs more. Power line communication (PLC) [15–18] and the remote-control scheme of micropower wireless communication have advantages in practical applications due to the convenient installation. However, the cost of such a solution is still high, which is not conducive to its promotion. Table 1 lists the characteristics of these four options.

**Figure 2.** Common traditional remote control schemes: (**a**) 0–10 V or pulse-width modulation (PWM); (**b**) digital addressable lighting interface (DALI); (**c**) traditional alternating current (AC) grid power line communication; (**d**) traditional wireless.


**Table 1.** Features of common traditional remote control schemes.

From the perspective of installation, the micropower wireless communication scheme needs to consider factors such as antenna and electromagnetic interference, which is greatly affected by space, and the PLC scheme is simpler. If the PLC solution can be further simplified, the cost and installation aspects are more advantageous. However, the traditional PLC solution is mainly used for alternating current (AC) mains grid, such as remote meter reading [19–21] and other applications. In the AC mains grid, PLC technology is relatively mature, and it is difficult to have major technological breakthroughs in a short period of time. It is difficult to reduce costs significantly. If power electronics can be used to transmit information while energy is being converted, the PLC module in Figure 2c may no longer be needed and the system cost may be greatly reduced. In the AC mains grid, since the existing transmission and distribution schemes are already very mature, it is difficult to implement communication using power electronics technology. However, if a direct current (DC) grid or an AC microgrid is constructed, it is easy to realize communication while transmitting DC power in the grid.

The LED lighting system based on DC grid has received attention. In [22] an indoor LED smart lighting system was proposed based on DC grid, as shown in Figure 3. The system uses an AC/DC converter to change AC mains to DC bus, and a number of distributed DC/DC LED drivers are connected to the DC bus. The system implements intelligent control and energy saving, but with the DALI communication protocol, a separate control line is still required. A similar DC bus architecture is also proposed in [23].

**Figure 3.** Traditional LED lighting system technology based on direct current (DC) grid: (**a**) Traditional networked LED system based on DC grid; (**b**) Traditional DC grid PLC technology; (**c**) the drive signal waveform of host switch M and the waveform of bus voltage Ubus.

PLC in the DC grid has also been studied in recent years, and this technology can eliminate the control line in Figure 3a. A novel DC PLC solution was proposed in [24], which is cheaper for small-scale power line communication applications. Figure 3b,c show the basic principle, as shown in the waveform: when the host switch M is turned on, the voltage Ubus goes high, representing logic 1. When switch M is turned off, voltage Ubus goes low, representing logic 0. The circuit works in the structure of the buck circuit, and the energy is stored in the output capacitor C of the slave. The change of the voltage Ubus during the energy transfer is detected by the slave, and the simultaneous transmission of energy and signals is realized. However, due to the influence of parasitic parameters

on the transmission line, the switching device of the circuit is subject to greater voltage stress than the conventional buck circuit.

Some papers have proposed DC PLC schemes [25–29], but they all need additional communication lines. They bring larger parasitic parameters and cause front-stage metal-oxide-semiconductor field effect transistor (MOSFET) high current spikes and damage when the MOSFETs are working at high frequency. So the front-stage MOSFETs need better performance requirements. They are more complicated if used for LEDs.

In order to overcome the problems of the above two types of research, this paper proposes a remotely controlled LED lighting system similar to the DC grid structure of Figure 3a, but with the control line omitted. In this system, an AC/DC bus converter converts the mains into a DC bus, and multiple distributed LED drivers are connected to the DC bus. The AC/DC DC bus converter receives the user's control command and modulates it into the DC bus voltage. The DC bus waveform changes to a square wave containing the high and low changes of the address information and the command information. The LED driving power source corresponding to the address receives energy from the DC bus and demodulates commands such as turning on the light, turning off the light, dimming, etc. In order to make the waveform of AC/DC DC bus converter have better rising and falling edge, this paper adopts the half-bridge topology with variable modal control. In the modulation process, the circuit works in buck mode and boost mode. Distributed LED drivers have DC/DC circuits and very simple demodulation circuits that dissipate energy and information from the DC bus.

With this remote control scheme, the following problems are solved:


Compared with the conventional schemes described above, this scheme is simpler and costs less. This paper verifies the feasibility of this technology by experiments.

#### **2. Light-Emitting Diode (LED) Networked Drive Technology Based on Direct Current (DC) Grid Power Line Communication (PLC)**

#### *2.1. System Architecture*

The specific architecture of the LED lighting system proposed in this paper is shown in Figure 2a. It includes a control center, an AC/DC bus converter, a DC bus, and a distributed LED driver. The control center sends control signals to the LEDs to the AC/DC bus converter. This type of technology is relatively mature and can be used for wireless communication such as a General Packet Radio Service (GPRS). The bus converter converts the AC mains into a DC bus voltage vbus with a maximum value of 48 V, and modulates the information to be transmitted into the bus voltage to make it high and low DC levels. The high voltage represents logic 1 and the low voltage represents logic 0. The DC bus is the transmission line, and the distributed LED driver as the load extracts energy from the DC bus drives the LED light source and demodulates the signal from the bus.

#### *2.2. New DC Power Line Carrier Energy and Information Demodulation Principle*

The master/slave communication mode is between the AC/DC bus converter and the distributed LED driving power source. The former is the master, the latter is the slave, and the DC bus is used as the medium to provide energy and transfer information to the slave.

The LED driver power supply includes three parts: an energy demodulation circuit, a signal demodulation circuit, and a DC/DC converter. The energy and signal demodulation circuits are both half-wave rectification circuits, as shown in Figure 4a. Taking the *j*th LED driving power supply in Figure 4a as an example, the energy demodulating circuit is connected in series with the DC/DC converter, and the output of the signal demodulating circuit is connected to the control circuit of the DC/DC converter. The difference between the two is that the energy demodulation circuit's output capacitance Cpj has a large capacitance value. When the vbus voltage is 0, the energy of the DC/DC converter of the latter stage can still be supplied for a period of time, that is, vpj is maintained within the allowable ripple voltage range to keep the circuit working properly.It remains stable for a long time; the output capacitance value Csj of the latter is small. When the vbus voltage is 0, vsj is discharged through the resistor Rsj and quickly falls to 0, so that the change of vsj is consistent with the change of vbus. Taking the waveform in Figure 4b as an example, the process of demonstrating a remote dimming operation has the following stages:

t1: The output of the AC/DC bus converter is 48 V DC, and the load is full power. During this time, the bus converter receives the *j*th LED drive power dimming command from the control center to address Aj.

t1–t2: The bus converter modulates the information into the DC bus, and the bus voltage vbus changes to the waveform shown in Figure 4b. All LED drive power supplies receive the command, but only the *j*th addresses Aj. The drive power source executes the dimming command. The total power on the busbar drops from time t3 when the command is executed. The communication protocol can adopt a mature scheme such as RS232 or a custom scheme.

**Figure 4.** Networked control LED system based on DC grid PLC: (**a**) system architecture diagram; (**b**) system key waveforms.

#### *2.3. Working Principle of Bus Converter Based on Variable Modal Control*

The key device for system energy and information modulation is the AC/DC bus converter. Figure 5a,b shows a schematic diagram and the corresponding buck and boost working modes. The circuit is divided into two stages. The first stage is a power factor correction (PFC) circuit to achieve a high power factor. The output is a fixed DC voltage Vg as the input of the second stage.

The second stage is a half-bridge circuit, the output is a DC bus, and the DC bus is connected to several LED driving power sources. The LED driving power can be regarded as the active load of the second-stage half-bridge circuit, and the total equivalent power is pLED. D1 and D2 are body diodes of the half-bridge circuit MOSFETs M1 and M2, respectively. The control circuit has a single-chip microcomputer (MCU), which samples the output voltage vbus through the sampling resistors R1 and R2, and RBoostcs and RBuckcs are sampling resistors, respectively sampling the inductor currents in boost and buck modes.

In different situations, the half-bridge circuit operates in buck mode or boost mode. Figure 5c shows the main waveforms of these two modes.

t0–t1: The AC/DC bus converter does not send a signal to the LED driver, and its output voltage is constant DC 48 V. The upper tube M1 is operated as a high-frequency switch, the lower tube M2 is stopped, the half-bridge circuit operates in buck mode as shown in Figure 5a, and the body diode D2 of the M2 acts as a freewheeling diode of the buck circuit. The bus converter charges capacitor C2, which supplies energy to the distributed LED driver.

t1–t11: The bus converter receives the command and modulates it into the bus voltage vbus, causing it to change to high and low DC levels. Defining the signal Sin passed, when Sin is logic 0, the bus converter operates in boost mode, and when Sin is logic 1, the bus converter operates in buck mode. When in boost mode, the upper tube M1 stops working, and M2 operates as a high-frequency switch. The body diode D1 of the M1 operates as a freewheeling diode of the boost circuit, as shown in Figure 5b. At this time, the energy on the bus voltage vbus across the output capacitor C2 is quickly transferred to the half-bridge input capacitor C1, and the level rapidly drops to zero. Since the LED driving power supply in Figure 4a has diodes Dpj and Dsj, the change in bus voltage does not affect the energy and signal demodulating circuits in the LED driving power supply.

**Figure 5.** Work principles of bus converter: (**a**) circuit principle of buck mode; (**b**) circuit principle of boost mode; (**c**) working waveform.

The half-bridge circuit adopts different working modes, so that in buck mode, the bus voltage vbus across capacitor C2 can rise rapidly; in boost mode, the bus voltage vbus across capacitor C2 can be quickly reduced. There are three advantages to using this method of variable mode control:


t12–: After the drive power supply executes the dimming command, the total pbus power on the bus is reduced.

As shown in Figure 5a,b, it is divided into two modes, buck and boost. Due to the poor reverse recovery performance of the body diode of the MOSFET, the circuit uses boundary current mode (BCM) regardless of buck or boost mode. The control circuits of both modes are controlled by ST L6562. In buck mode, M2 is always off and its body diode D2 operates as a freewheeling diode of the buck circuit. In the main circuit, the signal ZCDBuck that controls M1 turn-on, the peak current signal CSBuck that controls M1 turn-off, and the output voltage signal VoBuck are sampled into the buck circuit controller. In boost mode, M1 is always off, and its body diode D1 acts as a freewheeling diode of the boost circuit. In the main circuit, the signal ZCDBoost that controls M2 turn-on and the peak current signal CSBoost that controls M2 turn-off are sampled into the boost control circuit.

In the t4–t10 time of Figure 5c, the specific working waveforms of the two working modes are given. At time t4, the transmitted signal Sin is still high, ENBuck is high, and ENBoost is low, indicating that the circuit is in buck mode, M1 is operational, M2 is disabled, and its drive signal Vg2 is always low. The body diode D2 of M2 operates as a freewheeling diode of the buck circuit. The energy flow of the circuit flows from capacitor C1 to C2, as shown in Figure 5a.

$$\mathbf{v\_g} - \mathbf{v\_{bus}} = \mathbf{L} \frac{\mathbf{i\_{Lpk}}}{\mathbf{t} \mathbf{s} - \mathbf{t\_4}} \tag{1}$$

where iLpk is the peak value of the inductor current during this period.

t5–t6: M1 is turned off, the inductor current drops, the body diode D2 of M2 continues to flow, CSBoost is negative voltage, and the half-bridge midpoint voltage Vds2 is low. The voltage and current in the circuit satisfy Equation (2), and the circuit gain relationship still satisfies the law of the buck circuit, as in Equation (3).

$$\mathbf{v}\_{\rm bus} = \mathbf{L} \frac{\mathbf{i}\_{\rm Lpk}}{\mathbf{t}\boldsymbol{\epsilon} - \mathbf{t}\boldsymbol{\varepsilon}} \tag{2}$$

$$\mathbf{v\_{bus}} = \frac{\mathbf{t\_5} - \mathbf{t\_4}}{\mathbf{t\_6} - \mathbf{t\_4}} \cdot \mathbf{v\_{\%}} \tag{3}$$

t6–t7: The circuit repeats the working process of the t4–t6 switching cycle until time t7, the transmission signal Sin becomes low level, ENBuck is low, and ENBoost is high, indicating that the circuit is in boost mode; M2 can work, M1 is disabled, and its drive signal Vg1 is always low. The body diode D1 of M1 operates as a freewheeling diode of the boost circuit. The energy flow of the circuit flows as shown in Figure 5b from capacitor C2 to C1.

t7–t8: M2 is turned on, the inductor current rises in the reverse direction, CSBuck is negative voltage, and the half-bridge midpoint voltage Vds2 is low. The voltage and current in the circuit satisfy the law of the general boost circuit, as shown in Equation (4).

$$\mathbf{v\_{bus}} = \mathbf{L} \frac{-\mathbf{i\_{Lpk}}}{\mathbf{t\_8} - \mathbf{t\_7}} \tag{4}$$

t8–t9: M2 is turned off, the inductor current drops, the body diode D1 of M1 continues to flow, CSBuck is negative voltage, and the half-bridge midpoint voltage Vds2 is high. The voltage and current in the circuit satisfy Equation (5), and the circuit gain relationship still satisfies the law of the boost circuit, as in Equation (6).

$$\mathbf{v\_g} - \mathbf{v\_{bus}} = \mathbf{L} \frac{-\mathbf{i\_{Lpk}}}{\mathbf{t}\rho - \mathbf{t}s} \tag{5}$$

$$\mathbf{v}\_{\mathfrak{F}} = \frac{\mathbf{t}\_{\mathfrak{Y}} - \mathbf{t}\_{\mathfrak{Y}}}{\mathbf{t}\_{\mathfrak{Y}} - \mathbf{t}\_{\mathfrak{k}}} \cdot \mathbf{v}\_{\text{bus}} \tag{6}$$

t9–t10: The circuit repeats the working process of the t7–t9 switching cycle until t10, because the voltage on C2 is already very low, meaning that most of the energy on C2 is fed back to C1.

The working principle of the bus converter described above is that the modal control of the circuit realizes the transformation of the high and low levels on capacitor C2 to achieve the purpose of simultaneously transmitting energy and information.

#### *2.4. Distributed LED Drive Power DC/DC Converter Working Principle*

The distributed LED drive power directly drives the light source and demodulates the communication information from the DC bus. The driving power source is divided into an energy demodulating circuit, an information demodulating circuit, and a DC/DC converter. The principles of the first two have already been introduced. Here, the working principle of the DC/DC converter is introduced.

In theory, there are many solutions for implementing the DC/DC converter of the driving power supply. This paper introduces the principle of demodulation energy and information by taking the buck circuit as an example. Figure 6 shows the schematic and key waveforms of the DC/DC converter in the distributed drive power supply of Figure 4a.

**Figure 6.** Principle of distributed drive power DC/DC converter: (**a**) schematic diagram; (**b**) key waveform.

The DC/DC converter uses a buck circuit and operates in a critical mode. Due to the critical mode, the output current io and the peak value iLDpk of the inductor current iLD satisfy the following relationship:

$$\mathbf{i}\_{\rm o} = \frac{1}{2} \mathbf{i}\_{\rm LDpk} \tag{7}$$

According to Equation (7), the output current io can be made constant by controlling iLDpk to be constant. The control circuit is implemented by chip L6562. The specific working process is as follows:

t1–t2: The enable signal EN given by the microcontroller allows the DC/DC converter to operate. The MOSFET MD is turned on and the inductor current rises. The voltage and current in the circuit meet the following equation:

$$\mathbf{V\_P} - \mathbf{v\_o} = \frac{\mathbf{L\_d} \cdot \mathbf{i\_{LDpk}}}{\mathbf{t\_2} - \mathbf{t\_1}} \tag{8}$$

t2–t3: At time t2, the voltage on the sampling resistor RCS reaches the threshold value Vref of comparator comp1, comp1 gives a positive level, and the output level of the RS flip-flop becomes low, so that the MD is turned off. At this time, the diode DD starts freewheeling, and the inductor current decreases. At time t3, since the inductor current drops to zero, the ZCD voltage drops, and the comparator comp2 output is high, causing the RS flip-flop output to be high, and the drive circuit starts driving the MD to conduct and begins to enter the next switching cycle. During this period, the voltage and current in the circuit satisfy Equation (9), and the circuit gain relationship still satisfies the law of the buck circuit, as in Equation (10).

$$\mathbf{v}\_{\rm o} = \frac{\mathbf{L}\_{\rm d} \cdot \mathbf{i}\_{\rm LDpk}}{\mathbf{t}\_{3} - \mathbf{t}\_{2}} \tag{9}$$

$$\mathbf{v}\_{\rm o} = \frac{\mathbf{t}\_{2} - \mathbf{t}\_{1}}{\mathbf{t}\_{3} - \mathbf{t}\_{1}} \cdot \mathbf{V}\_{\rm P} \tag{10}$$

The t3–t4 circuit repeats the switching cycle state of t1–t3. It should be pointed out that Vref is given by the single-chip circuit and Vref changes, according to Equation (7); the output current also changes.

t4–t7: The single-chip circuit receives the dimming command from the bus converter, reduces the Vref voltage, and reduces the output current io of the DC/DC converter.

t7: The single-chip circuit receives the shutdown command from the bus converter, turns the enable signal EN to low, the DC/DC converter stops working, and the output current is zero.

Through the working principles described above, the distributed LED driving power supply can drive the LED load according to the command sent by the bus converter.

#### **3. Experimental Verification**

The principles of system operation were introduced in the previous section, and the working process of the bus converter and distributed LED driver power supply is analyzed in detail. In order to verify the technology mentioned in this section, this paper establishes a verification system as shown in Figure 4a. The physical diagram is shown in Figure 7. System parameters are shown in Table 2.

**Bus converter Transmission line Distributed driver**

**Figure 7.** Picture of demo system.



#### *3.1. Bus Converter Working Principle Verification*

The main task of the bus converter is to convert the AC mains into the bus of the DC grid. During the transition, the DC grid output voltage is modulated into a signal that is communicated to the distributed LED drive power source, allowing both signal and energy to be delivered simultaneously. This experiment mainly verifies this function.

Figure 8 shows the input and output waveforms of the bus converter. It can be seen that under the 220 V AC mains, the bus converter converts it into a 48 V DC bus vbus. After the communication signal Sin is modulated into the vbus, the Sin changes, and the vbus also changes in the same waveform to achieve simultaneous transmission of energy and information. Due to the presence of the PFC circuit, the power factor is approximately 1, and the input voltage and current waveforms are approximately the same.

**Figure 8.** Input and output waveforms of bus converter.

According to the above description, when the DC bus voltage vbus is high, the bus converter is in buck mode, and the output vbus is high. When vbus is low, in order to quickly reduce the voltage of the bus converter output capacitor C2, the bus converter goes into boost mode, so that the C2 energy is quickly transferred to the bus converter input capacitor C1 for continued use in the next cycle. Figure 9 shows the main waveforms of the modal transformation. The pass signal Sin is the same as the enable signal of buck mode. It can be seen from the waveform that in steady state, the bus converter operates in buck mode, the signal Sin is high, the drive Vg1 of the upper tube M1 is working, the drive Vg2 of the lower tube M2 is low, and the output voltage vo is constantly 48 V. When the bus converter receives the command, it modulates the signal Sin into the output bus, causing it to become a square wave with the same high and low conversion as Sin. At this time, buck and boost modes of the bus converter are switched according to the transmission signal.

**Figure 9.** Main waveforms of bus converter during steady state and communication.

The output transformer of the bus converter is continuously charged and discharged during the signal modulation process. It is essentially the energy flow relationship between the input capacitance C1 of the bus converter and the output capacitor C2. Figure 10 shows the experimental relationship of energy flow. It can be seen from Figure 10 that in buck mode, the buck sampling resistor voltage vBuckcs is positive, the boost sampling resistor voltage vBoostcs is negative, and the bus converter output capacitor C2 is charged. In boost mode, the buck sampling resistor voltage vBuckcs is negative, the boost sampling resistor voltage vBoostcs is positive, and the bus converter output capacitor C2 energy is transferred to the input capacitor C1.

**Figure 10.** Energy flow relationship in the process of bus converter modal transformation.

As mentioned above, since the bus converter needs to use a body diode of a MOSFET of half-bridge topology as a freewheeling tube in either buck or boost mode, the reverse recovery capability of the MOSFET body diode is poor, in order to reduce this. The effect is that the circuit uses a critical mode. Figure 11a,b shows the key waveforms of the bus converter in buck and boost mode during communication. In buck mode, the sampling resistor voltage vBuckcs and the half-bridge midpoint voltage vds2 are visible, and the circuit operates in a critical mode, avoiding the loss caused by the reverse recovery of the body diode D2 of the lower tube M2. In boost mode, the sampling resistor voltage vboostcs and the half-bridge midpoint voltage vds2 are visible, and the circuit operates in a critical conduction mode, avoiding the loss caused by the reverse recovery of the body diode D1 of the upper MOSFET M1. This experiment verifies the working principle of the bus converter.

**Figure 11.** Critical conduction mode waveforms of the bus converter under (**a**) buck mode and (**b**) boost mode.

#### *3.2. Distributed LED Driver Power Supply Working Principle Verification*

The main task of the distributed LED drive power source is to receive the energy of the DC bus and demodulate the information. This experiment mainly verifies this function.

Figure 12 shows the main waveforms of the energy and information demodulation of the distributed LED driver power supply during communication. It can be seen from Figure 6 that when the enable signal EN is 1, the MOSFET MD starts to work. As shown in Figure 12, vgs is a high-low level transition of the driving signal of the MOSFET MD, enabling the distributed LED driver to operate, so that the bus voltage vbus is high level. At this time through the modulation and demodulation of the signal circuit, so that vs is also high level, and in the energy circuit, vp is also high level output. When the enable signal EN is 0, the MOSFET MD stops working. At this time, the driving signal vgs of MD is kept low. At this time, in the signal circuit, vs is also low, and in the energy circuit, due to the capacitance of Cp, as shown in the figure, is slightly dropped and can be maintained within the allowable ripple voltage range to keep the circuit working properly.

**Figure 12.** Distributed LED drive power energy and information.

In this section, the distributed LED driver power supply uses a critical conduction mode buck circuit, and the output current io is a constant current source. Figure 13 shows the operating waveform of the drive power supply. vcs is the voltage of sampling resistance Rcs, Rcs is used to sample the current flowing through it. Figure 6a shows, when MD is turned on, the current of inductor LD flows through Rcs. vgs is the drive signal of MD, and vds is the voltage between drain and source of MD. The circuit operates in a critical conduction mode, avoiding the loss caused by the reverse recovery of the body diode D1 of the upper MOSFET M1, and reducing circuit losses.

**Figure 13.** Critical conduction mode waveforms of distributed LED driver.

The LED driving power supply executes the command after demodulating the information on the DC bus. Figure 14 shows the waveform of the action performed after a drive power supply receives a light-off command. When the bus converter receives the command from the control center, it means to turn off the light, so that vbus changes as shown in Figure 14, this signal represents the command "LED off at a certain address". Through the modulation and demodulation of the circuit, the signal is passed through the signal conditioning circuit to the LED driver at an address as shown in Figure 6a, so that it performs the light-off action, as shown in the CS waveform, and finally becomes a low level.

**Figure 14.** Execution command waveforms of distributed LED driver.

#### **4. Conclusions**

With common traditional lighting system remote control schemes like 0–10 V, PWM control, and DALI, two additional communication lines must be used, which brings installation inconvenience and costs more. Traditional PLC or wireless technologies do not need two communication lines. Although they are easy to install, they are not easy to popularize because of their high cost. A DC power grid based on the new power line carrier technology proposed in this paper enables the LED driving power source to have not only energy conversion capability, but also communication capability by using power electronics to realize communication technology. In order to realize the communication function of the driving power source, the proposed system includes a bus converter and a distributed driving power source. The bus converter modulates the information into the DC bus through variable modal control, from which the distributed drive power demodulates energy and information. In contrast with 0–10 V, PWM control, and DALI, this technology does not need communication lines, it is easier to install, and the cost is lower. Compared with the traditional PLC, its communication circuit is simpler, so the cost is lower. Compared with wireless technology, the radio frequency module can be omitted, so the cost is decreased and the installation is simpler. This technology not only simplifies the use of communication technology in application, but also reduces the difficulty of application. The prototype system validated the effectiveness of the technology. It is possible that this technology can also be used in other applications besides LED.

**Author Contributions:** Conceptualization, H.L. and J.H.; methodology, H.L.; software, H.L.; validation, H.L., J.H. and Z.L.; formal analysis, X.Z.; investigation, H.L.; resources, L.W.; data curation, J.H.; writing—original draft preparation, H.L.; writing—review and editing, H.L. and J.H.; visualization, H.L.; supervision, J.H.; project administration, Z.L.; funding acquisition, L.W.

**Funding:** This research was funded by National Natural Science Foundation Youth Project of China, grant number 51607060.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Nomenclature**


#### **References**


© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
