©shutterstock/isaart from simulations to experiments …by qing-chang zhong, yeqin wang, yiting...

by Qing-Chang Zhong, Yeqin Wang, Yiting Dong, Beibei Ren, and Mohammad Amin

The only constant is change—power systems worldwide are going through a paradigm change from centralized generation to distrib-uted generation; transportation systems are being electrified; and billions of lives in third-

world countries are awaiting low-cost sustainable elec-tricity. Control and power electronic technologies are

two common enablers to address these grand challenges. Empowering next-generation engineers with hands-on skills in control and power electronics has become a pri-ority for global higher education. However, setting up a suitable experimental system requires time, effort, and a broad range of expertise. This article aims to help researchers, university professors, graduate students, and engineers lower the barriers to go real from simula-tions to experiments for various power electronic sys-tems and improve the efficiency and productivity of

Go Real: Power Electronics From Simulations to

Experiments in HoursVersatile experimental tool for next generation engineers

©SHUTTERSTOCK/ISAART

2329-9207/20©2020IEEE52 IEEE POWER ELECTRONICS MAGAZINE zSeptember 2020

Digital Object Identifier 10.1109/MPEL.2020.3011300Date of current version: 15 September 2020

Authorized licensed use limited to: Texas Tech University. Downloaded on September 16,2020 at 20:32:57 UTC from IEEE Xplore. Restrictions apply.

September 2020 zIEEE POWER ELECTRONICS MAGAZINE 53

research, development, and educa-tion. It shows that it is possible to obtain experimental results within hours after completing simulations by adopting the SYNDEM Smart Grid Research and Educational Kit, which is a reconfigurable, open-source, multifunctional power elec-tronic converter with the capability of directly downloading codes from MATLAB/Simulink. This minimizes the time, cost, and efforts needed to develop hardware systems and re -moves the burden of coding. After briefly introducing the SYNDEM kit and highlighting the automatic code generation capability, two case studies will be illustrated: an ac motor drive and a dc-dc-ac con-verter for an integrated PV-storage system.

Barriers in Research Development and Education with ExperimentsControl and power electronics are two major enablers for the paradigm shift of power systems from centralized gener-ation to distributed generation, the electrification of trans-portation, and the transformation of billions of lives in third-world countries. For power systems or smart grids, a large number of active units including wind farms, solar farms, distributed energy resources (DERs), electric vehicles, energy storage systems and flexible loads are being integrated into power systems through power electronic converters [1], [2]. This imposes great challenges to the stability, scalability, reli-ability, security, and resiliency of future power systems [3], [4]. Hence, it is vital to develop advanced technologies so that these different players are able to take part in the regulation of future power systems in an autonomous and responsible way. For electrification of transportation, power electronic convert-ers are widely used in more-electric aircraft, all-electric ships, electric vehicles, spaceships, satellites, etc. The control of power electronic converters lies in the heart of these applica-tions and many other areas such as computers, telecommuni-cation, data centers, consumer electronics, industrial systems, lighting, motor drives, etc.

While advancing technologies for these applications is important to address the problems, another key is to pro-vide low-cost versatile tools to facilitate the research and development of technologies and to educate next-genera-tion engineers. A lot of education and training on the control of power electronics are simulation-based due to the lack of affordable and reconfigurable hardware platforms. The emergence of hardware-in-the-loop (HIL) simulations has made it easier to obtain simulation results that are close to real experiments. However, the price of HIL simulation sys-tems is still high. Moreover, while these simulations reflect the behavior of real systems to some extent, many practi-cal issues cannot be accurately modeled with simulations and numerical instability often occurs. Needless to say,

real experiments are the best way to reflect the dynamics and characteris-tics of real applications, and carry-ing out physical experiments should be an integrated part of training next-generation engineers and leaders in power electronics. In order to make this happen, two major barriers need to be lowered or better removed: the availability of suitable hardware plat-forms and the elimination of software coding burden. It usually takes sev-eral months for a skilled person to build an experimental system with

several iterations. Furthermore, different topologies usu-ally require different new hardware designs. As to software coding, it is often the job of another person – it is difficult for a hardware engineer to write codes. It often takes sev-eral months or longer for a beginner to fully understand the programming platform and the target machine. Moreover, code debugging can be very time-consuming.

This article aims to help researchers, university pro-fessors, graduate students, and engineers lower or even remove the barriers for carrying out physical experiments for control of power electronic-based systems. It will dem-onstrate that it is possible to obtain experimental results within hours after completing simulations by adopting the SYNDEM Smart Grid Research and Educational Kit (“the Kit” is used hereafter), which is a multifunctional, recon-figurable, and open-source power electronic converter with the capability of directly downloading codes from MAT-LAB/Simulink (Figure 1). As a result, the two major barriers mentioned above are lowered or even removed.

Introduction to the SYNDEM KitThe Kit is featured by MathWorks as a reconfigurable power electronic converter for research and education in smart grids [5]. The Kit can be reconfigured to obtain over 10 different power electronic converters, covering dc-dc converters and single-phase/three-phase dc-ac, ac-dc, and ac-dc-ac converters in the islanded or grid-connected

FIG 1 SYNDEM Smart Grid Research and Educational Kit. (Source: SYNDEM; used with permission.)

It is possible to obtain experimental results within hours after completing simula-tions by adopting the SYNDEM.


54 IEEE POWER ELECTRONICS MAGAZINE zSeptember 2020

mode. As a result, it can be used to quickly set up research, development, and education platforms for differ-ent applications, such as solar power integration, wind power integration, machine drives, energy storage sys-tems, and flexible loads. Moreover, there is no need to spend time on coding because it adopts the widely-used Texas Instrument (TI) C2000 ControlCARD and is equipped with the automatic code generation tools of MATLAB, Simulink, and TI Code Composer Studio (CCS), making it possible to generate experimental results within hours from simulations. It comes with complete interface details and sample implementations, based on which users can easily test their own control algorithms and enhance their hands-on skills.

The main features of the Kit include:■■ Reconfigurable to obtain 10+ different power electronic

converter topologies■■ Capable of directly downloading control codes from

MATLAB/Simulink■■ Ideal for research in smart grid, microgrid, renewable

energy, EV, energy storage, etc.■■ Compatible with utilities around the world with 120 V or

230 Vac, 5A current■■ Versatile communication interfaces, such as RS485 and

CAN, for SCADA■■ Multiple digital-to-analog (DAC) channels for easy debug-

ging and monitoring of internal signals■■ Suitable for parallel, grid-tied, or islanded operation with

single or multiple kits.

Hardware StructureAs shown in Figure 1, the Kit consists of one control board and one power board. The control board is on top of the power board and there are two auxiliary power supplies located beneath the power board. The TI C2000 Control-CARD is inserted at the back of the control board. The con-trol board has the capability of connecting two power boards. An additional power board can be added to the Kit to carry out experiments for two three-phase converters with one controller, for example, back-to-back converters in permanent magnet synchronous generator (PMSG) or dou-bly-fed induction generator (DFIG)-based wind power gen-eration system (WPGS).

The power board, with its main power circuit shown in Figure 2, contains a three-leg IGBT module A1P35S12M3 and its driver circuits, relay, current sensors, voltage sen-sors, inductors, capacitors, and fuses. The power board accepts pulse-width modulation (PWM) signals from the control board and transfers analog voltage/current/tem-perature signals to the control board through two flat rib-bon cables. The IGBT module contains six 1200V 35 A switching devices in three legs with a common posi-tive bus. It has a built-in negative temperature coefficient (NTC) thermistor for temperature measurement. The double circles in Figure 2 represent banana sockets on the power board, which allows the reconfiguration of the main

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power circuit with banana wires into different power elec-tronic converter topologies. There are two dc-bus 470 µF 450 V capacitors, C76 and C77, which can be configured in series or in parallel to meet the requirement of the volt-age rating or the capacitance. There are three sets of LC filters with inductors L1, L2, and L3 and capacitors C78, C79, C80, with one set connected to the output of the IGBT module directly and the other two sets reconfigurable. Moreover, inductor L2 and capacitor C78 can be placed freely. A relay is included to facilitate grid connection. All the inductor currents and capacitor voltages, as well as the dc-bus current and voltage, are measured and sent to the control board. In addition, two voltages on the grid side are measured to facilitate grid connection. The power board is also equipped with ac fuses F2, F3, and F4, dc fuse F1, NTC thermistors VR1, VR2, and VR3 for protection and a pre-charging resistor R61 for the pre-charging of capaci-tors. The power board is also equipped with a standalone 1600 V 35 A three-phase diode bridge with a 470 µF 450 V capacitor, making it possible to power the dc bus from an external ac grid.

The power board can be easily reconfigured to obtain different topologies, such as dc-dc con-verters (including buck, boost, and buck-boost converters), PWM-controlled rec-tifiers (single-phase and three-phase), inverters (single-phase and three-phase), i -converters, Beijing converters, dc-dc-ac converters, ac-dc-ac back-to-back converters (single-phase and three-phase), and more. It can be used for islanded oper-ation or grid-tied operation. Multiple kits can be used to build up microgrids.

The control board includes a TI C2000 TMS320F28335 ControlCARD, signal condi-tioning circuits for analog voltage/current/

temperature signals from the power board, 22-channel 12-bit analog-to-digital (ADC) inputs, 12-channel PWM out-puts, 4-channel 12-bit DAC outputs, 4 switches, 4 program-mable LEDs, SPI, RS485 and CAN interfaces, and protection circuits. Up to two power boards can be connected to one control board. Any internal signals can be sent out through the DAC outputs for monitoring on an oscilloscope, saving the need of using expensive differential probes. While the Kit is designed for power electronic applications, it can be adopted for general control systems as well.

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Automatic Code GenerationThe Kit is equipped with automatic code generation, as illustrated in Figure 3. The software code or the source code can be developed in the MathWorks modeling envi-ronment, i.e., with MATLAB® and Simulink®, which is a graphical programming environment so there is no need for users to learn sophisticated programming skills. Through MathWorks Embedded Coder®, the target sup-port for TI C2000 and the link to TI Code Composer Stu-dioTM (CCS), ANSI/ISO C/C++ codes can be automatically generated for TI CCS. Then, through the compile & link process in the TI CCS environment, executive codes can be generated for downloading to TI C2000 ControlCARD in the Kit. More features about automatic code genera-tion can be found in [6].

It is worth noting that there is no need for users to touch any C/C++ or executive codes during software develop-ment. The control algorithms can be pre-verified in the MATLAB/Simulink environment based on simulations. The same control algorithms can be inserted into a pro-vided software code template as illustrated in Figure 4. After configuring the measurement interfaces, protection thresholds, PWM channels, DAC channels, and communi-cation channels, the code can be downloaded to the Kit, which makes it possible to obtain experimental results within hours. Note that any signals inside the code, includ-ing the external signals measured, can be monitored with oscilloscopes through DAC channels and in MATLAB/Simulink through RS485 communication. A host graphical user interface (GUI) file in MATLAB/Simulink is provided for this purpose.

Two Case Studies

I. AC Motor DriveThe ac motor drive system for a permanent magnet syn-chronous motor (PMSM) is shown in Figure 5, where the Kit is configured as a three-phase motor controller to drive an Anaheim Automation EMJ-04 PMSM. A 60 V dc source is used to power the dc bus of the Kit. An AmpFlow E30-150 dc generator powering four parallel-connected resis-tors (total 0.25 X) is used as the mechanical load for the PMSM. An oscilloscope is used to monitor and record sys-tem operation waveforms through the DAC outputs from the Kit, with additional data monitored on a host computer through RS485. The quadrature encoder pulse (QEP) inter-face on the Kit is used to measure the rotor position angle.

The wire configuration of the main power circuit for the PMSM drive is shown in Figure 6, where the LC filters are not used. This can improve the accuracy when calibrating the rotor position. The PMSM is directly connected to the three outputs of the IGBT module after the current sensors. The back EMF of line-line voltages vab and vca are measured through sensing points between A2a and A3, and between C2a and C3, respectively. The inductors do not affect the voltage measurement, because there are no currents

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passing through them. The two dc capacitors are connected in parallel. The detailed wiring procedures are to:■■ Connect the dc bus: TD1–TD3, TD5–TD6, and TE6–Bus-■■ Connect the dc-bus capacitors: TD5–TD2, TD6–TE1, and

TE2–Bus-■■ Connect the phase lines: TB6–TB5, and TA6–TA5■■ Connect the dc source: Terminal Bus+ to dc positive, and

Terminal Bus- to dc negative

■■ Connect outputs: TA4 to Phase A, TB4 to Phase B, and TC4 to Phase C for three-phase PMSM

■■ Connect the back EMF measurements: TB4–TA7, and TA4–NThe conventional vector control to regulate the torque or

the speed of an ac motor, as shown in Figure 7, is adopted. A digital switch Siq is used to select the torque control mode or the speed control mode. The three-phase motor cur-rents are converted into d–q currents, id and iq, which are

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regulated through d–q voltages ud and uq, respectively. For a surface-mount PMSM, there is a linear relationship between the electromagnetic torque Te and the q-axis current iq as

k iT T qe = so the current reference id) can be calculated

through the torque reference as i T kd e T=) )_ i in the torque control mode or generated through the speed PI controller in the speed control mode. The d-axis current reference id

) can be set as 0 to fulfill the maximum torque per ampere (MTPA) requirement. More information about the coeffi-cient kT can be found in [7]. The PI control of the d–q currents generates the voltages ud and uq, which are converted to six space-vector pulse width modulation (SVPWM) signals to drive IGBT after inverse-Park and inverse-Clarke transfor-mations and an SVPWM signal generator. More information about PMSM and vector control can be found in [8].

The main controller shown in Figure 7 together with addi-tional ADC measurements, QEP measurement, DAC outputs, and protection functions can be implemented in MATLAB/Simulink and directly downloaded to the TI C2000 TMS320F28335 ControlCARD for execution. A video of the PMSM control based on the Kit can be found in [9].

Note that the rotor position angle is required for both the Park and inverse-Park transformations. Through the built-in ABI incremental encoder of the PMSM and the QEP decoder on the Kit, the rotor position can be obtained after compensating the initial rotor position offset. Thanks to the DAC function of the Kit, this can be done with ease. Based on the characteristics of the PMSM, the initial rotor position offset of the PMSM is the intersection point of back EMF vab and vca when the signal vab – vca crosses zero from positive to negative. It can be calibrated as follows:

180 W PVSystem

SYNDEM Smart GridResearch and Educational Kit

120 Vrms, 60 Hzac Output

Human MachineInterface

1.8 kWhBattery

FIG 11 Structure of the SPEED system [10]. (Source: Texas Tech University; used with permission.)

(a)

(b)

FIG 10 A sustainable, portable, and efficient electricity deliv-ery (SPEED) system built with the Kit. (a) Front and (b) back view. (Source: Texas Tech University; used with permission.)



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■■ Connect wires as shown in Fig-ure 6, with TB6–TB5 and TA6–TA5 disconnected to avoid the back EMF of the PMSM charging the dc-bus capacitors

■■ Use the dc power supply to power the dc motor to drive the PMSM in the same rotation direction as in the PMSM driving mode

■■ Keep the PMSM rotating at a con-stant speed, e.g., around 833 rpm in this test

■■ Record the waveforms of the mea-sured rotor position and the back EMF sent out from the DAC out-puts on an oscilloscope

■■ The initial rotor position offset is the angle of the intersection point from the zero positionFor example, the curves shown in

Figure 8(a) indicate that the speed of the PMSM is constant with the same amplitudes of the back EMF at each cycle and the zoomed-in results of the measured rotor position and the back EMF shown in Fig-ure 8(b) indicate that the initial rotor position offset is 145°.

The experimental results of the ac motor drive are shown in Figure 9(a) for operation in the torque control mode and Figure 9(b) for operation in the speed control mode. In both cases, the performance is satisfactory and the d-axis current id is well regulated around zero.

II. PV-Battery SystemFigure 10 illustrates a photovoltaic (PV)-battery system built up with the Kit at Texas Tech University (TTU). It is a sus-tainable, portable, and efficient electricity delivery (SPEED) system [10], capable of providing speedy access to electric-ity, e.g., during emergencies or after natural disasters. It can be operated in the islanded mode or the grid-connected mode. The system, as shown in Figure 11, consists of a 180 W PV source, a 1.8 kWh battery pack, a Kit, and a data monitoring subsystem. The solar panels absorb and convert solar energy into dc electricity and the battery is used as a storage. The Kit provides the power electronic conversion for both the PV source and the battery pack with a standard utility-level ac output. The data monitoring subsystem is designed for monitoring and recording real-time data of the SPEED system through RS485 communication. In order to enhance the portability of the SPEED system, all hardware components, including the PV panels, the battery pack, the Kit, and the data monitoring subsystem, are mechanically mounted on a mobile cart. Students are able to improve their skills significantly by building up such a system.

As shown in Figure 12(a), the Kit is configured as a dc-dc boost converter cascaded with a single-phase dc-ac converter, with the wire configuration of the main power

circuit shown in Figure 12(b). The detailed wiring procedures are to:■■ Connect the dc bus: TD1–TD3,

TD5–TD6, and TE6–Bus-■■ Connect the dc-bus capacitors:

TD5–TD2, and TE2–Bus-■■ Connect W-leg: TA1–TA3, TA5–TA6,

TA1–TE1, and TA7–Bus-■■ Connect V-legs: TB6–N■■ Connect the PV input: Terminal A to

PV positive, and Terminal Bus- to PV ground;

■■ Connect the battery: Terminal Bus+ to Battery positive, and Terminal Bus- to Battery negative;

■■ Connect the ac output: TC2 to load hot, and Terminal N to load neutral

■■ Connect the utility-grid: Terminal C to grid hot, and Terminal N to grid neutral.The SPEED system can be oper-

ated in the islanded mode with grid-forming capabilities for outdoor activities or emergency/disaster reliefs

and in the grid-connected mode with the energy generated by the PV source sent to the utility-grid. Advanced control algorithms are developed and downloaded to the TI C2000 TMS320F28335 ControlCARD to control both the dc-dc boost converter and the dc-ac converter. For example, the robust droop control technology [11] is adopted for the islanded operation of the SPEED system, extremum-seeking (ES)-based maximum power point tracking (MPPT) for max-imum power acquisition from the PV source, and robust grid-integration technology [12] for the dc-ac converter. A video for the field test of the system can be found in [13].

Figure 13 shows some experimental results when the SPEED system is operated in the grid-connected mode. After the system starts, the PV power increases to the maxi-mum value, around 160 W quickly, due to the fast conver-gence of the ES-based MPPT. Then, the real power sent to the grid follows well the real power extracted from the PV source while the battery power is kept almost around zero in the steady state. There is a negative battery power at the beginning because the dc-ac converter is enabled after the dc-dc converter. The grid reactive power is always regulated around 0 to keep the unity power factor. The variations in the real power extracted from the PV are due to clouds.

ConclusionsIn this article, it is shown that the barriers to go real from simulations to experiments in hours for power electronic systems can be considerably lowered or even removed by adopting a reconfigurable, open-source, multifunctional power electronic converter with the capability of directly downloading codes from MATLAB/Simulink. This will help researchers, university professors, graduate students, and

Barriers to go real from simulations to experiments in hours for power electronic systems can be consid-erably lowered or even removed by adopting a reconfigurable, open-source, multifunctional power electronic con-verter with the capa-bility of directly down-loading codes from MATLAB/Simulink.



engineers shorten the learning curve and improve the pro-ductivity of research and education. The SYNDEM Smart Grid Research and Educational Kit is taken as an example to demonstrate this, with two case studies – one for an ac motor drive and the other for an integrated PV-storage sys-tem. The Kit can be adopted for lab-bench systems as well as standalone research projects. While the kit is ideal for power and energy-related applications, it can also be used for other general control systems as well because of its ver-satile interfaces and computational power.

About the AuthorsQing-Chang Zhong ([email protected]) received the Ph.D. degree in control and power engineering from Imperial Col-lege London, London, U.K., in 2004 and the Ph.D. degree in control theory and engineering from Shanghai Jiao Tong Uni-versity, Shanghai, China, in 2000. He is the Max McGraw Endowed Chair Professor in Energy and Power Engineering at Illinois Institute of Technology and the Founder and CEO of Syndem LLC, Chicago, USA. He is a Fellow of IEEE and IET, a Distinguished Lecturer of IEEE Power Electronics Society, IEEE Control Systems Society and IEEE Power and Energy Society, and the Vice-Chair of IFAC TC Power and Energy Systems. He served as AE for IEEE TAC/TIE/TPELS/TCST/Access/JESTPE. He proposed the synchronized and democratized (SYNDEM) grid architecture for the next-gen-eration smart grid to unify the interaction of power system players with the grid for autonomous operation through the synchronization mechanism of synchronous machines, with-out relying on the communication network. His research focuses on power electronics and advanced control systems theory, together with their seamless integration to address fundamental challenges in power and energy systems.

Yeqin Wang ([email protected]) received the B.Eng. degree in Automotive Engineering from China Agricultural University, Beijing, China, in 2009, the M.Eng. degree in Automotive Electronics from Clean Energy Automotive Engineering Center, Tongji University, Shanghai China, in 2012, and the Ph.D. degree in Wind Science and Engineering from the National Wind Institute, Texas Tech University, Lubbock, in 2019. He is director of technology at Syndem LLC, Chicago, IL. His research interests include power elec-tronics control, renewable energy, and microgrids.

Yiting Dong ([email protected]) received the B.Eng. degree from the School of Automation Engineering, Univer-sity of Electronic Science and Technology of China (UESTC), Chengdu, China, in 2014 and the M.Eng. degree in control science and engineering from UESTC, in 2017. He is pursuing the Ph.D. degree in the Department of Mechanical Engineering, Texas Tech University, Lubbock, TX. His cur-rent research interests include power electronics control, renewable energy, and microgrids.

Beibei Ren ([email protected]) received the B.Eng. degree in Mechanical & Electronic Engineering and the M.Eng. degree in Automation from Xidian University, Xi’an, China, in 2001 and in 2004, respectively, and the

Ph.D. degree in the Electrical and Computer Engineering from the National University of Singapore, Singapore, in 2010. She is an Associate Professor in the Department of Mechanical Engineering at Texas Tech University. She is also a faculty affiliate of the National Wind Institute, Texas Tech University. Her research focuses on control, microgrids, smart grid, and power electronics. She had successful experiences in building microgrid testbeds at different scales for both research and education. She received the TechConnect National Innovation Award for a microgrid control technology. She serves as AE for IEEE Transactions on Industrial Electronics and IEEE Access. She is a senior member of IEEE.

Mohammad Amin ([email protected]) received the Ph.D. degree in engineering cybernetics from Norwegian University of Science and Technology, Norway, in 2017. From 2017 to 2019, he was a Senior Research Asso-ciate with the Department of Electrical and Computer Engi-neering, Illinois Institute of Technology, Chicago. Currently, Amin is an Associate Professor with the Department of Electric Power Engineering at Norwegian University of Sci-ence and Technology. His research interest focus on digital control of power electronics for cyber-physical systems, wind and solar energy integration, microgrid, smart grids, and robust control theory for power electronics systems.

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