Bidirectional AC Sources / Sinks

Bidirectional AC sources and loads combine a programmable AC power supply, grid simulator, and electronic AC load in a single system. They can supply a device under test (DUT) with controlled electrical energy and absorb energy returned by it. Regenerative systems feed the absorbed energy back into the AC mains, enabling efficient and reproducible four-quadrant testing without separate source and load equipment.

The ET System portfolio includes the ZGX bidirectional AC/DC source and load, the compact N75500 regenerative grid simulator, the ESA system for single- and three-phase grid simulation, and the high-bandwidth KGS four-quadrant AC/DC power amplifier. Depending on the series, the systems support single-phase, split-phase, and three-phase operation as well as AC, DC, and regenerative load modes.

Typical applications include testing grid-connected inverters, onboard chargers, UPS systems, electric drives, photovoltaic inverters, energy storage systems, and other power electronics. Bidirectional AC systems are also used for grid simulation, compliance testing, automated test equipment (ATE), and dynamic research applications. The appropriate system is selected according to phase configuration, voltage, current, source and sink power, frequency range, bandwidth, grid-simulation functions, regenerative capability, interfaces, and mechanical integration.

How to Select a Bidirectional AC Source and Load

Selecting a suitable bidirectional AC system starts with the electrical requirements of the device under test (DUT) in both source and load operation. In addition to voltage, current, and power, the required phase configuration, frequency range, dynamic response, grid-simulation functions, regenerative capability, automation interfaces, mains connection, and mechanical integration should be considered.

• Phase configuration: Determine whether the DUT requires single-phase, split-phase, or three-phase operation. For three-phase applications, check whether each phase can be controlled independently and whether balanced and unbalanced grid conditions must be simulated.
• Voltage, current, and power in both directions: Define the required RMS voltage, peak voltage, current, apparent power, active power, and short-term overload capability for source and load operation. Source and sink ratings may differ, and maximum voltage, current, and power may not always be available simultaneously.
• Four-quadrant and AC/DC operation: Verify whether the system must support positive and negative voltage and current as well as AC, DC, or AC+DC output modes. Four-quadrant operation is required when energy flow and polarity can change during the test.
• Frequency range and bandwidth: Define the required fundamental frequency and higher-frequency signal components. Standard grid simulation may only require frequencies around 50 or 60 Hz, while dynamic testing, power amplification, or power hardware-in-the-loop applications may require considerably greater bandwidth. For highly dynamic applications, the KGS AC/DC power amplifier may be suitable.
• Dynamic response: Check voltage and current slew rates, response time, settling time, overshoot, minimum event duration, and the transition between source and load operation. Fast and seamless transitions are particularly important for inverter, drive, and energy-storage testing.
• Grid simulation: Verify support for programmable voltage and frequency sequences, phase-angle changes, voltage dips, interruptions, ramps, phase imbalance, harmonics, and arbitrary waveforms. Also check whether the required IEC, EN, grid-code, or application-specific test functions are available.
• Power factor and reactive power: Define the required active and reactive power as well as the power-factor range. Check whether both leading and lagging current and the simulation of inductive, capacitive, and nonlinear load conditions are required.
• Regeneration and mains connection: Regenerative systems return absorbed energy to the AC mains instead of converting it entirely into heat. Check the available mains voltage, phase configuration, input current, connection type, regenerative power limits, and facility requirements for energy recovery.
• Accuracy and power quality: Check programming and measurement accuracy for voltage, current, power, frequency, and phase angle as well as resolution, total harmonic distortion (THD), ripple, noise, and data acquisition rate.
• Interfaces and automation: For automated test equipment (ATE), verify remote-control commands, sequence functions, trigger options, external analog control, software compatibility, and available interfaces such as LAN, CAN, RS232, RS485, USB, SCPI, and digital I/O.
• Protection and safety: Consider overvoltage, overcurrent, overpower, and overtemperature protection, interlocks, emergency shutdown, output discharge behavior, isolation, grounding concept, and protection against accidental contact.
• Parallel operation and scalability: For higher current or power requirements, verify whether the selected series supports parallel or master-slave operation. Check the maximum number of units, combined operating area, power distribution, communication, and required cabling.
• Mechanical integration and cooling: Consider dimensions, weight, rack installation, airflow, cooling requirements, AC and DC connections, mains connection, and the available space for safety and switching components.

If energy is required in only one direction, a conventional programmable AC power supply or electronic AC load may be sufficient. For application-specific test benches, ET System combines sources, loads, measurement equipment, safety technology, power distribution, and control systems through test system integration. For support with selecting a suitable configuration, contact our technical sales team.