TIDUF64A December   2023  – August 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
    2. 1.2 PV Input with Boost Converter
    3. 1.3 Bidirectional DC/DC Converter
    4. 1.4 DC/AC Converter
  8. 2System Design Theory
    1. 2.1 Boost Converter
      1. 2.1.1 Inductor Design
      2. 2.1.2 Rectifier Diode Selection
      3. 2.1.3 MPPT Operation
    2. 2.2 Bidirectional DC/DC Converter
      1. 2.2.1 Inductor Design
      2. 2.2.2 Low-Voltage Side Capacitor
      3. 2.2.3 High-Voltage Side Capacitor
    3. 2.3 DC/AC Converter
      1. 2.3.1 Boost Inductor Design
      2. 2.3.2 DC-Link Capacitor
  9. 3System Overview
    1. 3.1 Block Diagram
    2. 3.2 Design Considerations
      1. 3.2.1 Boost Converter
        1. 3.2.1.1 High-Frequency FETs
        2. 3.2.1.2 Input Voltage and Current Sense
      2. 3.2.2 Bidirectional DC/DC Converter
        1. 3.2.2.1 High-Frequency FETs
        2. 3.2.2.2 Current and Voltage Measurement
        3. 3.2.2.3 Input Relay
      3. 3.2.3 DC/AC Converter
        1. 3.2.3.1 High-Frequency FETs
        2. 3.2.3.2 Current Measurements
        3. 3.2.3.3 Voltage Measurements
        4. 3.2.3.4 Auxiliary Power Supply
        5. 3.2.3.5 Passive Components Selection
    3. 3.3 Highlighted Products
      1. 3.3.1  TMDSCNCD280039C - TMS320F280039C Evaluation Module C2000™ MCU controlCARD™
      2. 3.3.2  LMG3522R030 650-V 30-mΩ GaN FET With Integrated Driver, Protection and Temperature Reporting
      3. 3.3.3  TMCS1123 - Precision Hall-Effect Current Sensor
      4. 3.3.4  AMC1302 - Precision, ±50-mV Input, Reinforced Isolated Amplifier
      5. 3.3.5  ISO7741 Robust EMC, Quad-channel, 3 Forward, 1 Reverse, Reinforced Digital Isolator
      6. 3.3.6  ISO7762 Robust EMC, Six-Channel, 4 Forward, 2 Reverse, Reinforced Digital Isolator
      7. 3.3.7  UCC14131-Q1 Automotive, 1.5-W, 12-V to 15-V VIN, 12-V to 15-V VOUT, High-Density > 5-kVRMS Isolated DC/DC Module
      8. 3.3.8  ISOW1044 Low-Emissions, 5-kVRMS Isolated CAN FD Transceiver With Integrated DC/DC Power
      9. 3.3.9  ISOW1412 Low-Emissions, 500kbps, Reinforced Isolated RS-485, RS-422 Transceiver With Integrated Power
      10. 3.3.10 OPA4388 Quad, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      11. 3.3.11 OPA2388 Dual, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      12. 3.3.12 INA181 26-V Bidirectional 350-kHz Current-Sense Amplifier
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Note
    3. 4.3 Test Setup
      1. 4.3.1 Boost Stage
      2. 4.3.2 Bidirectional DC/DC Stage - Buck-Mode
      3. 4.3.3 DC/AC Stage
    4. 4.4 Test Results
      1. 4.4.1 Boost Converter
      2. 4.4.2 Bidirectional DC/DC Converter
        1. 4.4.2.1 Buck Mode
        2. 4.4.2.2 Boost Mode
      3. 4.4.3 DC/AC Converter
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Authors
  13. 7Revision History

3.2.3.5 Passive Components Selection

As Figure 3-11 shows, multiple passive components are present in the DC/AC stage. The theory behind the design of each passive component is described in detail in the following section. The EMI filter design comprises of two boost inductors, two common-mode chokes, and a network of CX and CY safety capacitors.

TIDA-010938 Block Diagram DC/AC FilterFigure 3-11 Block Diagram DC/AC Filter
  • Boost Inductor Selection

The design of the boost inductor is essential for finding an optimal EMI filter that results in maximum filter efficiency and minimum filter volume. The primary role of the boost inductor is to filter out the switching frequency harmonics and it is necessary to keep in mind, the calculation of the current ripple and choose material of the core that is able to tolerate the calculated current ripple. The boost inductors are further split to have better common-mode filtering capability and better filtering capacity for the individual switching nodes.

The emission mask for many standards starts at 150kHz; therefore, selecting a switching frequency below 150kHz is always a good design practice. In this design, a switching frequency of 87kHz was selected for the H-Bridge Bipolar and HERIC DC/AC topologies. For H-Bridge in unipolar modulation scheme, by topology definition, there is a doubling of switching frequency effect at the output EMI filter. Hence, a switching frequency of 43.5kHz was employed. By selecting an operating frequency of 87kHz, the first harmonic does not require significant attenuation but only the successive ones such as the 2nd, 3rd, and so forth. A current ripple factor of 30% was selected for the boost inductor, when having 230VAC output. The inductance value was calculated by using Equation 16.

Equation 16. L≥520 V4×4600 W230 V×2×0.3×87000 Hz

An inductance value equal to 176μH was calculated. Bourns 145453 was selected and this is an inductor rated 87μH, 20 RMS. The inductor is split in both legs to have better common-mode capability. In general, the boost inductor contributes to the differential and common-mode noise attention.

  • CX Capacitance Selection

Class-X (CX) and Class-Y (CY) capacitors are safety-certified capacitors that are usually used in AC line filtering applications which help to minimize the generation of EMI. Furthermore, X capacitors are connected between the line and neutral, to protect against differential mode interference, and Y capacitors are designed to filter out common mode noise. Common mode choke coils have the use of suppression of common mode noise.

CX are the capacitors connected between line-to-line or line-to-neutral. The aim of these capacitors is to attenuate the differential mode noise injected from the DC/AC into the grid. The value of these capacitors is a trade-off between reactive power provided to the grid and the differential mode attenuation. By default, the reactive power injected into the grid is equal to Equation 17.

Equation 17. Q=Vg2×2πfg×CX

At 10% load, a power factor equal to 0.9 (26°) has been set up as requirement. Thus, leading to limit the quantity of reactive power, given by Equation 18.

Equation 18. Qmax=0.1×Pnom ×tan∅ 

The maximum value of capacitance can be calculated from Equation 17and Equation 18 and is equal to 13.5μF. Two CX capacitors, respectively, with values of 4.7μF each were selected.

  • CY Capacitance Selection

It is necessary to detect small leakage currents (typically 5–30 mA) and disconnect quickly enough (<30 ms) to prevent device damage or electrocution. Certain standards for the leakage current issue mention that PV systems with the transformer-less inverter must discontinue their service if the leakage current value of 100mA can persist up to 0.04s. With the total capacitance of 13.6nF going towards the ground, the leakage current through the Y capacitors can be calculated with Equation 19.

Equation 19. IY-Cap=V×2πfg×CY

For the grid voltage of 230VRMS, this value comes out to be 0.98 mA < 30 mA, hence the system requirements are met.

  • EMI Filter Design

The following EMI filter was designed to attenuate both the differential-mode and common-mode noise injected into the grid. The EMI filter can be analyzed in the common-mode and differential-mode domains. From the EMI filter shown in Figure 3-12, it is possible to derive the equivalent common- and differential-mode circuits as shown respectively in parts a) and b), where Lσ represents the leakage inductance of the common-mode choke.

TIDA-010938 EMI Filter DesignFigure 3-12 EMI Filter Design
  • a. Equivalent differential-mode model
  • b. Equivalent common-mode model

The first critical frequency to be attenuated is the 174kHz. The 87kHz was not considered because that value is not in the EMI mask.

Table 3-4 Attenuation Required in DM/CM Modes
ATTENUATIONVALUE
Differential-Mode Attenuation at 174kHz87dB
Common-Mode Attenuation at 174kHz83dB

An EMI filter with the values listed in Table 3-5 was designed.

Table 3-5 EMI Filter Values
PARAMETERVALUE
L187μH

CX1

4.7μF
Lcm1Lcm 4mH, Lσ 4μH
CX24.7μF
Lcm2Lcm 4mH, Lσ 4μH
CY26.8nF

Two Bourns CMCs (047708) were used in this EMI filter.

  • DC-Link Capacitance

In single-phase applications, power ripple is present coming from the grid, and can cause voltage ripple on the DC-link. The DC-link capacitor value is calculated using Equation 20.

Equation 20. Cout≥4600 W2×400×π×50 Hz×46 V

A total capacitance of 800μF was calculated for the 4.6kW, 400V, and 50Hz operating condition. Five of ALH82(1)161DD600 devices was selected for this application. Also note that the ripple current through the electrolytic capacitors can be handled by the model of capacitors used.