Evaluating the load-capacity of an inverter drive circuit is critical to verify proper operation after connecting the IGBT module. Many latent faults that do not appear under no-load conditions — such as OC (over-current) trips or IGBT destruction during operation — stem from insufficient drive capability.

Two practical test approaches are available: a simple resistive-load method for repair work, and an oscilloscope-based method for professional analysis. Select according to available tools.

Method 1 Simple Resistive-Load Test (for rapid repair diagnostics)

This low-cost workshop method simulates IGBT gate loading to directly measure drive current.

1.Pre-requisites

Disconnect the drive board from the high-voltage main circuit for safety.

Bypass protection circuits: short the Vce-sense pins to the drive-supply 0 V rail to avoid false fault-locking of PWM pulses.

2.Test setup

Components: 3 W power resistor, digital multimeter with DC mA range.

Resistor value: match or approximate the IGBT gate resistance RG (typically 15 Ω ~ 51 Ω); ensure adequate power rating to prevent burnout.

Wiring: Connect the DC mA multimeter in series with the power resistor. Attach this series branch across the drive output terminals (GG-EE).

Tip: Some technicians connect the current meter in parallel with the resistor; the core objective is to insert current measurement into the gate loop.

3. Measurement & criteria

Power up the drive board, trigger run/stop commands, and capture static and dynamic current readings for each channel.

4.Fault isolation

If one channel shows abnormal drive current under load:

Measure positive- and negative-drive supply voltages. Significant voltage drop → suspect degraded filter electrolytic capacitors or faulty rectifiers.

If supply voltages remain normal → fault lies within signal path. Inspect drive optocouplers and push-pull amplifying transistors for ageing or elevated internal resistance.

Method 2 Oscilloscope-Based Professional Analysis (R&D & in-depth troubleshooting)

For quantitative assessment of PWM waveform integrity and overall system performance, use an oscilloscope (e.g. Tektronix IMDA / Fluke MDA series).

1.Key measured parameters

· V/Hz ratio: determines motor torque. Excessive ratio causes motor overheating; insufficient ratio yields poor torque output.

· Voltage modulation & dv/dt: characterise PWM rising-edge steepness. Excessive dv/dt stresses motor winding insulation.

· Total Harmonic Distortion (THD): input-side THD quantifies grid pollution.

· Voltage & current unbalance: three-phase amplitudes should be closely matched with 120° phase separation. Unbalance indicates potential rectifier or motor defects.

2.Probe & safety requirements

· Mandatory high-voltage differential probe: drive circuits are floating-potential. Never use passive single-ended probes for phase-voltage measurement, as short-circuit damage will occur.

· Current probe for dynamic current waveform capture.

· Degauss current probes and perform Deskew calibration before testing to eliminate time-offset errors between voltage and current channels for accurate power computation.

3.System-level efficiency measurement (advanced)

Use oscilloscope math functions to acquire input (grid-side) and output (motor-side) power and calculate real-time drive-system efficiency for energy-performance evaluation.

Summary

· Repair troubleshooting: adopt the resistive-load + multimeter method. Focus on current balance across all six drive channels.

· In-depth performance validation: oscilloscope with high-voltage differential probes. Evaluate waveform quality and overall system metrics.