SLVAFJ9 March   2023

 

  1.   Abstract
  2. 1 Table of Contents
  3.   Trademarks
  4. 2 Introduction
  5. 3 EMI Frequency Ranges
  6. 4 Passive EMI Filters for High-Power, Grid-Tied Applications
  7. 5 Active EMI Filters
  8. 6 Generalized AEF Circuits
  9. 7 Selection of the CM Active Filter Circuit
  10. 8 The Concept of Capacitive Amplification
  11. 9 Practical AEF Implementations
  12. 10Practical Results
    1. 10.1 Low-Voltage Testing
    2. 10.2 High-Voltage Testing
  13. 11Summary
  14. 12References

10.2 High-Voltage Testing

Figure 10-4 and Figure 10-5 show the measured CM EMI performance with the TPSF12C1-Q1 single-phase AEF IC using the power stage of the High-Efficiency GaN CCM Totem-Pole Bridgeless Power Factor Correction (PFC) Reference Design (TIDM-1007 shown in Figure 4-2), which is a 3.3-kW single-phase bridgeless PFC converter [3] with LMG3410 GaN power devices switching at 100 kHz.

GUID-20230223-SS0I-VPZS-TD9H-8TBQDGGXVQKV-low.pngFigure 10-4 EMI Performance With TIDM-1007: AEF Disabled vs. Enabled Using the Same Filter
GUID-20230223-SS0I-QLXP-H4JF-VCF8N0GBDDZC-low.pngFigure 10-5 EMI Performance with TIDM-1007: A Small-Choke AEF Design Compared to a Large-Choke Passive Filter

As evident in Figure 10-4, the AEF provides 15 to 30 dB of CM noise attenuation in the low-frequency range (150 kHz to 3 MHz), which enables a filter using 1- and 4-mH nanocrystalline chokes to achieve an equivalent CM attenuation performance as a passive filter design with two 12-mH chokes, as shown in Figure 10-5. To support a fair comparison, these chokes derive from the same component family with a similar core material (vendor: Würth Elektronik). In addition, the smaller-size chokes of the AEF-based design provide better attenuation at frequencies above 10 MHz given the lower intrawinding parasitic capacitance.

Figure 10-6 shows photos of the filters used for the EMI results presented in Figure 10-5. The AEF enables a 52% reduction in box volume of the CM chokes, as highlighted in Figure 10-7.

Figure 10-6 Size Reduction Enabled by AEF: Passive Filter (a); Active Filter (b)
Figure 10-7 Area, Volume, Cost and Weight Reduction Enabled by AEF (a); Choke Size Comparison (b)

Table 10-1 captures the applicable parameters for the CM chokes highlighted in Figure 10-6. The AEF achieves a 60% total copper loss reduction at 10 ARMS (PCU = 6 W – 2.36 W = 3.64 W, neglecting the winding resistance increase from temperature rise), which implies lower component operating temperatures and improved capacitor lifetimes.

Table 10-1 CM Choke Component Details for the Passive and Active Filter Implementations
Filter CM Choke Part Number Quantity LCM (mH) RDCR (mΩ) fSRF (MHz) Size (L × W × H, mm) Mass (g) PCu (W)
Passive 7448051012 2 12 15 0.8 23 × 34 × 33 36 3.0
Active 7448041104 1 4 8.5 10 19 × 28 × 28 17 1.7
7448031501 1 1 3.3 40 17 × 23 × 25 10 0.66

Figure 10-8 provides impedance curves for the CM chokes to highlight the smaller-size components that have a higher self-resonant frequency and improved high-frequency performance. As an example of the higher CM impedance at high frequencies because of the lower intrawinding capacitance, the impedance of the grid-side CM choke at 30 MHz increases from 150 Ω to 1.1 kΩ (when going from 12 mH in the passive design to 1 mH in the active design). The × and o markers shown at 10 MHz and 30 MHz in Figure 10-8 demarcate the respective impedances for passive and active designs. The higher choke impedance above 10 MHz for active designs largely obviates the need for grid-side Y-capacitors.

GUID-20230223-SS0I-XXW7-7NSB-Z5MVQKXPSV6J-low.png Figure 10-8 Impedance Characteristics of the Selected CM Chokes in the Passive Design (2 × 12 mH) and Active Design (4 mH and 1 mH)

As expected, horizontally mounted chokes in three-phase circuits can generally yield even larger percentage footprint reductions relative to the vertically mounted chokes common in single-phase designs.