Power electronic interface with de‐coupled control for wind‐driven PMSG feeding utility grid and DC load
2017; Institution of Engineering and Technology; Volume: 11; Issue: 2 Linguagem: Inglês
10.1049/iet-pel.2017.0347
ISSN1755-4543
AutoresC. Maria Jenisha, N. Ammasai Gounden, N. Kumaresan, Kadi BhagyaSri,
Tópico(s)Multilevel Inverters and Converters
ResumoIET Power ElectronicsVolume 11, Issue 2 p. 329-338 Research ArticleFree Access Power electronic interface with de-coupled control for wind-driven PMSG feeding utility grid and DC load Charles Maria Jenisha, Charles Maria Jenisha Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorNanjappagounder Ammasaigounden, Corresponding Author Nanjappagounder Ammasaigounden ammas@nitt.edu Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorNatarajan Kumaresan, Natarajan Kumaresan Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorKadi BhagyaSri, Kadi BhagyaSri Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this author Charles Maria Jenisha, Charles Maria Jenisha Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorNanjappagounder Ammasaigounden, Corresponding Author Nanjappagounder Ammasaigounden ammas@nitt.edu Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorNatarajan Kumaresan, Natarajan Kumaresan Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this authorKadi BhagyaSri, Kadi BhagyaSri Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, IndiaSearch for more papers by this author First published: 01 February 2018 https://doi.org/10.1049/iet-pel.2017.0347Citations: 10AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract A wind energy conversion system employing dq control has been proposed for extracting maximum power from a wind-driven permanent magnet synchronous generator (PMSG) and feeding it to a three-phase utility grid. The controller consists of a diode bridge rectifier, a dc–dc boost converter and a voltage source inverter (VSI). The grid synchronisation is achieved by controlling the VSI at the grid side. Besides supplying power to the ac grid, the proposed scheme also feeds a local dc load, as the dc link voltage is maintained constant. To evaluate the performance of proposed scheme, MATLAB/Simulink based model is tested under varying wind speeds. A proportional–integral controller is used for varying the duty ratio of the dc–dc converter to maintain the output dc voltage constant. The decoupled control algorithm for independent control of real and reactive power fed to the grid is implemented using dSPACE DS1103 controller. A steady-state analysis has been developed for predicting the value of duty cycle as well as the reference current for maximum power point tracking at a given wind velocity or rotor speed of PMSG. Experiments have been carried out on a 48 V, 750 W, 500 rpm PMSG and the test results are furnished to validate the developed scheme. Nomenclature peak phase voltage of the grid (V) d-axis voltage at the grid terminal (V) q-axis voltage at the grid terminal (V) d-axis current injected by the inverter (A) q-axis current injected by the inverter (A) angular frequency (rad/s) f grid frequency (Hz) proportional and integral gains of the current controller, respectively filter inductance (mH) R line resistance (Ω) on time resistance of the switches (Ω) desired time constant of the system (s) full load voltage of the PMSG (V) rated speed of the PMSG (rpm) N actual speed of the PMSG (rpm) voltage at the dc link (V) current at the dc link (A) n level of the boost converter root mean square value of grid voltage (V) root mean square value of grid current (A) 1 Introduction Due to rapid development in industrialisation and automation, global demand for electrical energy is increasing day by day. Fossil fuel which fulfils the major part of the energy demand will deplete in near future and therefore it is need of the hour to switch for an alternative source for energy. One such alternative source of energy is wind energy, which is an eminent source for electrical energy generation, due to the advances in wind generators, power electronic conversion techniques and integration. According to the utility point of view, wind energy conversion system (WECS) can be classified as stand-alone and grid tied. The squirrel cage induction generator (SCIG) is being widely used in such WECS due to its robust construction, absence of slip rings and brushes, small size and ease of maintenance. However, the basic problem with SCIG is that it demands more reactive power for its operation in addition to difficulty in voltage and frequency control for stand-alone applications. Power electronic converters had been used for smooth voltage and frequency control of stand-alone WECS [1, 2]. Subsequently, the need for extracting maximum power from the renewable energy sources started getting more emphasis and several schemes with power electronic interface have been proposed for grid-connected WECS with maximum power point tracking (MPPT) control employing SCIG [3, 4]. In the meantime, wound rotor induction machines have started emerging as a better choice for WECS in view of reduced power rating for the power converters which are connected at the rotor circuit of the machine [5]. Vijayakumar et al. [6] have proposed a control strategy for wound rotor induction generator (WRIG) based grid-connected system, employing only one insulated-gate bipolar transistor (IGBT) switch chopper and not requiring any mechanical sensors. Thus, with the emergence of WRIG, possibility of power being fed to the grid from both stator and rotor started arising and power could be extracted from super-synchronous as well as sub-synchronous operation of the generator. Hence, variable speed doubly fed induction generator (DFIG) based WECS started becoming more attractive for stand-alone and grid-connected applications [7-10]. The permanent magnet synchronous machines are now available which can replace induction machines due to the following advantages: (i) they do not have slip rings and brushes, (ii) neither dc supply nor excitation capacitors are required for voltage build up, (iii) there is no drop out speed, (iv) they operate at higher efficiency due to the absence of magnetising current and gear. In view of the above advantages, permanent magnet synchronous generator (PMSG) is widely preferred for stand-alone and grid-tied wind energy applications. The disadvantage is that both the output voltage and frequency will vary with varying wind speed, as in the case of SCIG. To overcome this, appropriate power electronic controller is to be used between the PMSG and the grid/load terminals for effective control. Various control strategies have been proposed for the operation of power electronic converter for both isolated and grid-connected PMSG-based WECS. Chan et al. [11] have presented the analysis and performance of a PMSG with diode bridge rectifier (DBR) connected across the stator terminals for supplying a stand-alone dc load. Wai et al. have focused on the development of a novel MPPT algorithm for PMSG-based grid-connected WECS with two stages of power conversion [DBR and voltage source inverter (VSI)]. Since there is no decoupled control scheme in the system, independent control of real and reactive power is not possible [12]. Chinchilla et al. [13] have presented a grid-connected PMSG-based WECS with two controlled converters with common dc link. Both the converters are controlled by dq control along with space vector modulation (SVM) technique. MPPT is achieved through controlling the machine side converter by sensing incident wind speed. However, the output of the second converter (grid side) has not been synchronised with utility grid. Singh et al. have proposed a dq control strategy for grid inter-connection of PMSG-based WECS with common dc link voltage of 500 V in simulation but conducted the experiment for scaled down dc-link voltage of only 75 V. MPPT is achieved by controlling the machine side converter via sensing the rotor speed of the wind turbine. The real and reactive power controls have been achieved [14]. Li et al. have presented a novel direct current vector control of PMSG-based grid-connected WECS. The system has two controlled converters with dq control along with sinusoidal pulse width modulation (SPWM) technique with the common dc-link voltage of 1500 V. The MPPT has been achieved by sensing the rotor speed of the wind turbine [15]. However, only simulation study has been carried out. Recently, Sayyed et al. [16] and Abdullah et al. [17] have proposed a PMSG-based WECS with two controlled converters with dq control and conservative power theory (CPT) control, respectively. All the above systems proposed for wind-driven grid-connected PMSG [12-17] have employed two controlled converters – one at grid side and other at machine side, both converters being controlled by two separate dq control techniques along with SPWM/hysteresis current controller (HCC)/SVM/CPT to achieve real, reactive power control, MPPT and grid synchronisation. In the above rectifier/inverter schemes, it is difficult to maintain the dc-link voltage constant at the required level as the wind velocity varies. The modulation index of VSI has to be varied beyond 1 at low wind velocities which will significantly reduce the switching frequency which in turn will increase the filter requirements. Pandurangan et al. have proposed a power transfer scheme for grid-connected renewable energy system using simple HCC at the grid side converter (GSC), in which independent control of real and reactive power is not possible [18]. Recently, Carlos Lumbreras et al. have proposed a three-stage power conversion configuration of PMSG-based one-phase grid-connected WECS. In this system, PMSG is connected with the grid through a rectifier, boost converter and an IGBT-based inverter. The maximum power extraction is achieved by controlling the boost converter. The inverter is controlled to pump the power from dc link to the grid using a proportional–integral (PI) controller along with PWM technique [19]. The advantage of this scheme over the previous schemes is that the control is simple. The limitation of this scheme is that it controls only a one-phase converter which feeds a one-phase utility grid. Further, there are no independent controls for real and reactive power. The proposed scheme in this paper consists of an uncontrolled converter (three-phase DBR) at the machine side to convert the variable ac voltage into variable dc, a dc–dc converter which is a multi-level boost converter (MBC) to fix the voltage at the dc link constant and a controlled converter (three-phase VSI) with decoupled control scheme at grid side for controlling the real power fed to the three-phase grid as well as the reactive power. The control is relatively simple as only one dq controller is required. A simple PWM control is used for the dc–dc converter for modulating the duty cycle of the gate pulse to maintain the output voltage (dc-link voltage) constant. This facilitates the scheme to supply dc load, besides feeding the grid. When the wind power is greater than the dc load, the excess power is fed to the grid. When the wind power is less than the dc load, the deficit power needed to satisfy the load is fed from the grid. Both real and reactive power control are achieved by employing dq control for the VSI. MPPT is also achieved employing a single current sensor at the dc link. The simulation results are validated by comparing with the experimental results. The grid voltage and current total harmonic distortion (THD) have been brought within the IEEE standards, below 5% for the grid current of 1 A or more. 1.1 Organisation of the paper Section 2 provides the block schematic of the proposed grid-connected WECS with details of MBC, VSI and MPPT controllers. The steady-state analysis which includes the determination of duty ratio (δ), id reference and iq reference is furnished in Section 3. Response of the proposed system in MATLAB/Simulink with dynamic change in wind speed is presented in Section 4. Section 5 presents the experimental results of both steady-state and dynamic response of the proposed scheme in dSPACE. The three different modes of operation of the proposed scheme with dc load are extended in Section 6. 2 Proposed scheme The block schematic of the proposed grid-connected WECS with MPPT controller is shown in Fig. 1. The system consists of: (i) wind turbine, (ii) PMSG, (iii) DBR, (iv) MBC and (v) three-phase VSI. The mechanical energy output of the wind turbine is converted into electrical energy through the PMSG. The variable output ac voltage of the PMSG is fed to DBR. The variable dc output of the DBR is boosted and maintained constant at 200 V using a two-level MBC and fed to the VSI through a dc link inductance (Ldc). The output of the VSI is fed to the three-phase utility grid. Fig. 1Open in figure viewerPowerPoint Block schematic of the proposed system As the PMSG used for experimental purpose in the proposed scheme is a low-voltage (48 V) high-current (15 A) machine, the need for MBC arises. It can be seen later in Section 5 that the range of duty ratio required to maintain the output voltage constant at 200 V for wind velocities varying from minimum to maximum values would be 0.3–0.6. The control algorithm for VSI is developed based on the decoupled control technique along with SPWM. The MPPT control is implemented by generating the reference current via simple Perturb and Observe (P&O) method, based on the dc-link current. As the dc-link voltage is maintained constant, any variation in wind power will get reflected only in the current. Hence, a single current sensor at the dc link is sufficient for MPPT control. An added advantage of this system is that it can feed dc loads as well which are connected at the dc link. 2.1 MBC controller The dc-link voltage (Vdc link) is sensed and compared against the reference voltage (Vdc link (ref)) of 200 V at which the dc-link voltage has to be maintained constant. The output signal obtained from the aforementioned comparison is fed to a PI controller to produce the error corrected signal, which is then compared with a saw-tooth waveform of frequency 2 kHz to produce the PWM gate pulse as shown in Fig. 2a for the IGBT switch in the MBC. Fig. 2Open in figure viewerPowerPoint Switching technique for the proposed system (a) MBC controller, (b) Closed-loop control model of the VSI converter, (c) VSI controller, (d) MPPT logic 2.1.1 Selection of PI controller parameters The PI parameters of the MBC controller are arrived at by manual tuning. Until the desired response is obtained kp and ki values are changed by observing system behaviour. For example, first ki value is set at zero and the value of kp is increased from zero till the system response varies around the set point. Then ki is assigned with some value and it is lowered until the system response is acceptable. The system response for obtained kp and ki values is verified by changing the set point. If the system begins to oscillate again, ki value is set to previous value and kp value is increased until the oscillation ceases. By using this method, the kp and ki values are obtained as 0.015 and 0.4, respectively, for MBC controller. The step value of kp and ki depends on the system response. 2.2 VSI controller The three-phase voltage (vabc) and current components (iabc) are measured at the grid terminals using voltage and current sensors, respectively. These three-phase time-varying quantities are converted to dc variables using three-phase rotating components to direct axis and quadrature axis (synchronously rotating reference frame components) conversion, i.e. abc to dq conversion. The three-phase instantaneous voltages are expressed as follows: (1)The three-phase voltage components are converted into dq0 components using the following expression: (2)For a balanced system, at any instant the zero sequence component v0 is zero because the sum of instantaneous values of the three-phase voltage is zero and it is expressed as follows: (3)The three-phase instantaneous currents (iabc) can also be converted into idq0 components using expression (2). The instantaneous real and reactive powers w.r.t. dq quantities are expressed as [20] (4) (5)It is clear from (4) and (5) that the real and reactive powers depend on both d and q-axis quantities. Hence, a decoupling is necessary to control the real and reactive power independently. For the vital decoupling, the q-axis voltage component is made zero by aligning the d-axis with the voltage space vector, which makes q-axis component as zero always. This condition is attained, if the voltage at the phase locked loop's (PLL's) connection point is considered as reference for dq frame transformations and then the space vector is aligned with the d-axis thus, vq = 0. The decoupled real and reactive power equations are expressed as (6) (7)From the above expressions, it is clear that for a particular d-axis voltage, the real and reactive powers are independently controlled by d-axis and q-axis current components, respectively. The control logic consists of d-axis current and q-axis current controllers, as mentioned above which independently control the active and reactive power. The MPPT allows to evacuate the maximum power which is available at the PMSG terminal for any wind speed. The d-axis current reference (idref) is computed from the MPPT control, so that the power generated from the PMSG matches the power fed to the grid instantaneously except the losses. In order to operate the inverter at unity power factor, the quadrature axis current (iqref) is set as zero. The reference currents are compared with the measured currents, the outputs of which are regulated by PI controller. The control equations in dq quantities are given as follows [20]: (8) (9)in which, (10) (11)The dq components are converted to three-phase components using dq0 to abc conversion, the expression for the same is given as follows: (12)The ua, ub and uc are the three-phase modulating signals which are compared with the triangular wave carrier signals. Thus, the SPWM is attained and the pulses are given to the inverter switching as shown in Fig. 2c. 2.2.1 Selection of PI controller parameters Fig. 2b represents the VSI controller used in the proposed system. The generic form of PI controller is . The open-loop transfer function of the system can be written as (13)where Lf is 60 mH, at any instant. The above transfer function has a stable pole at . Typically, this pole is fairly close to the origin and corresponds to a slow natural response [20]. To improve the open-loop frequency response, the pole can be cancelled by the zero of the PI compensator by choosing and . The closed-loop transfer function of the system can be expressed as (14)which is a first-order transfer function with the unity gain. has to be made small for a desired control response. The desired time constant chosen for the proposed system is 1 ms. Therefore Then substituting the obtained kp in the equation The above values of kp and ki are further fine-tuned to obtain the desired system response. Values of the kp and ki in the proposed VSI controller are 50 and 1000, respectively. 2.3 Maximum power point tracking The MPPT block tracks the maximum power at the PMSG using simple P&O method by sensing the current at the dc link. The present measured current at the dc link is Idc link (k) and the previous instant current is held for comparison by delaying it one unit Idc link(k − 1). If the present current Idc link (k) is greater than the previous instant current Idc link(k − 1), the perturbation is kept in the increment direction until it reaches the maximum power point and if the previous instant current is greater, then the next perturbation has to be in the opposite direction as shown in Fig. 2d. The idref is positive when the wind power available is in excess to feed the load at the dc link as well as the grid. When the wind power is not sufficient to supply the dc load, the deficit power is drawn from the grid by providing idref as negative to make the inverter to operate in rectification mode. 3 Steady-state analysis The duty ratio required for maintaining the constant voltage at the output of the boost converter can be obtained in terms of rotor speed of the generator. The variable ac voltage at the output terminals of PMSG is (15)The rectified voltage of the PMSG at the output of DBR is (16)Also the required values of idref and iqref of VSI for feeding maximum power to the grid are to be determined. 3.1 Determination of duty ratio The output voltage of the MBC which is the dc-link voltage can be obtained as (17)from which we obtain (18)The duty ratio required to obtain the dc-link voltage of 200 V at the rated wind velocity N = 500 rpm is calculated as 35%. The real, reactive and apparent power fed to the grid, respectively, can be expressed as (19) (20) (21)The IGBTs in the VSI are switched based on the ud and uq values, for feeding maximum power to the grid. 3.2 Determination of idref and iqref Fig. 3 shows the wind turbine characteristics and the maximum mechanical power (Pmech) at different wind speeds of the proposed system. From this figure, we can get the maximum power fed to the grid (Pgrid) after deducting the losses. By substituting this power (Pgrid) in (6), we can get the reference current to be given to the VSI controller for pumping available power to the grid for the corresponding rotor speed as depicted in Table 1. On the other hand, the reactive power is supplied from/to the grid by choosing an appropriate iqref at rated voltage as given in (7). The relation between the reactive power and q-axis current component is explained in detail in Section 5 along with the experimental results. Table 1. Steady-state performance of the proposed WECS operating at MPPT condition for different wind velocities Wind velocity, m/s Rotor speed, rpm Pre/Sim/Exp Stator voltage, V Stator current, A Rectifier voltage, V Rectifier current, A MBC duty ratio, % dc-link voltage, V dc-link current, A id reference, A Grid current, A Power fed to the grid, W 8 360 Sim 34.7 04.5 46.9 04.9 53 200 01.0 1.50 1.05 200 Exp 35.0 04.0 46.3 04.4 55 0.96 1.33 0.94 180 10 440 Sim 42.0 08.1 56.0 07.0 44 200 02.0 2.74 1.94 370 Exp 42.4 07.2 55.2 06.9 45 01.9 2.60 1.84 350 12 500 Sim 46.2 12.3 62.4 11.9 37 200 03.7 4.75 3.36 640 Exp 48.0 12.0 62.1 11.6 38 03.6 4.50 3.16 600 Sim: simulation, Exp: experimental. Fig. 3Open in figure viewerPowerPoint Wind turbine characteristics of the proposed system 4 Simulation results To validate the effective operation of the proposed system, simulation study has been carried out using a simpower systems toolbox in MATLAB software. The PMSG model in MATLAB has been used with ratings of the machine available in the laboratory (48 V, 500 rpm, 750 W). A wind turbine model available in the MATLAB is used to drive the PMSG. The mechanical torque output of the wind turbine varies with wind velocity. This torque is given as a negative value to the PMSG model as input. The wind turbine parameters used for MATLAB/Simulink model are shown in Table 2. The MATLAB simulation models of three-phase DBR, MBC and VSI are developed. Table 2. Wind turbine parameters for MATLAB/Simulink model Parameter Value nominal mechanical output power, Pm 750 W base wind velocity 12 m/s maximum power at base wind velocity 0.95 p.u. base rotational speed, N 500 rpm air density, ρ 1.205 kg/m3 moment of inertia, J 0.075 kg/m3 maximum power coefficient, Cp 0.48 pitch angle, β 0 tip speed ratio, λ 8.1 To ascertain the satisfactory working of the proposed system, simulation study has been carried out for different wind velocities and the results obtained from the steady-state performance are given in Table 1. It can be observed from this table that the MBC controller adjusts the duty ratio of the IGBT switch for maintaining the dc-link voltage at 200 V and MPPT controller varies the current reference to the VSI controller for tracking the maximum power available in the wind turbine as per the characteristics shown in Fig. 3. The variation in current reference adjusts the rotor speed of the generator in such a way that it captures the maximum power. Thus, the change in the wind speed results in variation in rotor speed which in turn causes change in stator voltage. Since DBR is used, the dc voltage output also varies with respect to the wind speed. In order to regulate the dc-link voltage at 200 V, the duty ratio of MBC is adjusted. Fig. 4 shows the simulated and experimental values of duty ratio corresponding to the rotor speeds. The values of the parameters kp and ki are chosen as 0.015 and 0.4, respectively, for MBC controller and 50 and 1000 for VSI controller, as explained in Section 2. Fig. 4Open in figure viewerPowerPoint Variation of duty ratio with respect to rotor speed Referring to Fig. 3, for extracting maximum power output of 750 W at 12 m/s wind velocity, wind turbine should be made to rotate at a rotor speed of 500 rpm. For achieving this, the change in current at the dc link is continuously monitored by sensing the dc-link current and as per P&O logic, and the corresponding reference current value of 4.75 A has been given to the VSI controller for extracting maximum power. The dynamic performance of the proposed scheme is evaluated initially without dc load by effecting step change in wind velocity from 9 to 11 m/s and from 11 to 10 m/s, each interval being maintained for 8 s. The resulting simulated waveforms of mechanical power (Pm), electrical power (Pe), real power pumped to the grid (Pgrid) and the dc-link voltage are furnished in Figs. 5a–e. It can be noticed from this figure that the proposed controller tracks the maximum power which reaches the steady state in 0.6 s for the given step change in wind velocity and that the dc-link voltage is maintained constant irrespective of the wind speed. Fig. 5Open in figure viewerPowerPoint Dynamic response of the proposed WECS for step change in wind speed, from 9 to 11 m/s and 11 to 10 m/s at 8 s interval 5 Experimental results A three-phase 48 V, 500 rpm, 750 W PMSG machine available in the laboratory has been used for experimentation. A separately excited dc motor of 230 V, 1500 rpm, 3.7 kW is chosen to drive the generator. Variable voltage variable frequency output from PMSG is converted to variable dc by the three-phase DBR (MD8TU6012 – 1200 V, 60 A) module. A two-level MBC has been built using IGBT (CT60AM – 900 V, 60 A) along with the signal conditioning circuit. The output of the MBC is given to the three-phase IGBT (SKM150GB12T4 – 1200 V, 150 A) based VSI through a dc-link inductor Ldc of 50 mH and the inverter output power is fed to the grid with appropriate filter inductance Lf of 60 mH to satisfy the grid standards. Two control loops are employed in the proposed system one for maintaining the dc-link voltage at 200 V and another for VSI to extract maximum power from wind turbine by adjusting the current reference, both control loops being implemented using dSPACE DS1103 controller. The dSPACE 1103 controller is a hardware interface which can generate DSP codes for MATLAB models. It consists of analogue-to-digital converter (ADC), digital-to-analogue converter (DAC) and R5232 serial interface. It downloads the codes to the controller board for executing the program in real time. Hence, this controller helps in generating required gate pulses for the power electronic converters and based on the external inputs from the voltage and current sensors, it seamlessly implements the complex closed-loop controls. It has to be mentioned here that the PLL hardware which is required for synchronising the output of VSI with the ac utility grid is also implemented by this controller. The voltage at the dc link is sensed through an external voltage transducer (LV 25-P) and the output of the voltage sensor is fed to the ADC with appropriate scaling factor. The ADC output is compared with the desired output voltage of 200 V. The error signal obtained is given to the PI controller which generates the control signal. This control signal is compared with a saw tooth carrier signal frequency of 2 kHz to generate the PWM pulse. The gate pulse thus obtained is available at the DAC output. This pulse is passed through optco-coupler (HCPL-3101) circuit which provides isolation as well as signal conditio
Referência(s)