Demonstration of a single-phase three-wire transformless inverter in a residential application. This model makes use of components from the Residential Energy library.
General Description
This model consists of a single-phase three-wire inverter made up of three IGBT Leg components. The inverter operates in grid-forming mode and represents a possible implementation of a battery inverter in a residential application. The circuit schematic is shown in Figure 1

Modeling
The single-phase three-wire inverter topology matches that of the three-phase inverter. The control logic and filtering component are designed for split-phase operation.
The control logic is decoupled into differential- and common-mode controllers. The differential-mode control drives legs 1 and 3 of the inverter and is designed to generate a 240 Vrms nominal sinusoidal output voltage between phases A and B. The common-mode controller operates in a voltage-balance mode and is responsible for balancing phase A and B voltages when unbalanced loading is present.
The operation of leg 2 enables balanced split-phase power generation without the need for a single-phase three-winding transformer. In practical applications, the ability to omit this transformer reduces system weight and volume requirements.
The inverter powers three distinct loads:
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Load 1: Connected between phase A and neutral (N).
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Load 2: Connected between phase B and neutral (N).
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Load 3: Connected directly between phases A and B.
Load values are presented in Table 1.
Load 1 |
Load 2 |
Load 3 |
|||
---|---|---|---|---|---|
Appliance |
Load (W) |
Appliance |
Load (W) |
Appliance |
Load (W) |
Microwave (PE) |
650 |
Refrigerator (PE) |
200 |
Dryer (heating)(ZIP) |
3000 |
Dryer (drum rotation)(ZIP) |
1000 |
Simulation
Figure 2 shows the SCADA Panel of the single-phase three-wire inverter example. Text boxes allow user-defined DC voltage Vin, AC reference voltage vd. The frequency and phase of the reference waveform are defined using the inputs or f and phi.

The differential-mode operation can be enabled using the "Enable Inverter" checkbox. The begins switching for legs 1 and 3 and generates the nominal 240 Vrms AC voltage. When inverter switching is enabled, the "Inverter ON" LED will light up green.
Information pertaining to the common-mode controller is presented in the "Balance Leg" group. Checking the "Enable Balance Leg" checkbox engages leg 2. An input for equivalent turns ratio is provided which represents the turns ratio of an equivalent transformer VAN:VAB. A value of 0.5 will attempt to balance voltages between phases A and B evenly.
Control Gains can be edited from a dedicated group on the SCADA Panel. The switching frequency for the three inverter legs can also be set from a dedicated widget. A default value of 20 kHz is used.
References
[1] S.J. Chiang, C.M. Liaw. (1994). Single-phase three-wire transformerless inverter. IEE Proceedings - Electric Power Applications, vol. 141, no. 4, pp. 197-205.