2.7. Principle of Operation

This section provides a general overview of the technology and power processing stages in the TS Series MagnaDC power supply. Fig. 2.20 and Fig. 2.21 provide a visual overview of the power supply’s main power and control stages. As illustrated, TS Series MagnaDC power supply are comprised of either master or master/slave modules. Master and slave modules have power ratings of 5 kW, 10 kW, 15 kW, 20 kW (4U), or 25 kW (4U). One module is required for 5 kW to 15 kW models, and one module is required for 20 kW to 25 kW 4U models with 380/415 Vac and 440/480 Vac 3-phase input. Two modules are required for 20 kW to 25 kW 6U models with 208/240 Vac 3-phase input, as well as for 30 kW to 50 kW models. Three modules are required for 75 kW models and four modules are required for 100 kW models. TS Series MagnaDC power supply have a number of shared feedback loops to ensure balance between modules. The details of the modules are described below.

Fig. 2.20 TS Series MagnaDC power supply functional block diagram for 5 kW to 15 kW models, and 20 kW to 25 kW 4U models with 380/415 Vac and 440/480 Vac 3-phase input

Fig. 2.21 TS Series MagnaDC power supply functional block diagram for 20 kW to 25 kW 6U models with 208/240 Vac 3-phase input, as well as for 30 kW to 100 kW models

2.7.1. Master Module

Power is fed through AC fuses and is distributed to the driver board, inrush limiter, and main 3φ contactor. The driver board contains a switching power supply and supplies power to the other printed circuit boards in the system. The inrush limiter is a step start device which is used to initially charge capacitors on the input DC bus and limit the inrush of current. The inrush limiter is initiated when the power supply is switched from a standby to a power state. After the charge cycle, the main 3φ contactor is energized and power is allowed to flow to the load. The optional EMI filter filters common mode and differential mode noise emanating from the supply.

Output power is controlled through a polyphase chopper. For the 15 kW master module, three choppers, phased 120° apart, provide a current source to a current fed inverter. The 10 kW TS uses two choppers, phased 180° apart, and the 5 kW supply uses only one chopper. The choppers are controlled with current mode, pulse width modulation (PWM). This modulation scheme provides a quick response for transients and filtering harmonics on the DC bus. As illustrated, chopper output current is monitored for balancing and for sensing overload current conditions. The polyphase chopper has been engineered to eliminate harmonic components minimizing currents circulating in the power supply.

The polyphase chopper produces a controlled DC bus which is connected to DC link inductors and current fed, IGBT medium frequency link inverter. The inverter, which operates at 400 Hz to 600 Hz, excites the main transformer at higher than normal line frequencies. This operation produces ohmic isolation between the input and output of the power supply using a transformer of dramatically reduced size.

The inverter operates with a 50% duty cycle and its frequency of operation is transparent to the performance of the power supply.

The output of the main power transformer is converted to DC via rectifiers. Low voltage versions of the TS Series power supply use midpoint diode configurations and higher voltage versions use bridge configurations.

The DC output voltage is filtered with a pie section filter. This, in combination with the DC link inductors, form a double stage inductive capacitive (LC) filter.

The gate driver board supports a synchronized modulation scheme which integrates power semiconductor switching of the switching power supply, polyphase chopper, and medium frequency link inverter.

The fuse/phase detector senses input line voltage on each phase and continuity of each fuse. Upon detection of a problem, the control board is signaled to shutdown the system. The control board, which is referenced to earth ground, contains optically isolated amplifiers to sense output voltage and current. This circuitry allows the output to be referenced ±1000 Vdc above earth ground.

The display board contains light-emitting diodes for displaying diagnostic conditions and provides an interface for meters and switches.

2.7.2. Slave Module

The slave module is very similar to the master module. Like the master module, output power is controlled through a polyphase chopper. For the 15 kW, 20 kW, and 25 kW slave modules, three choppers, phased 120° apart, provide a current source to the current fed inverter. The 10 kW TS power supply uses two choppers, phased 180° apart, and the 5 kW supply uses only one chopper.

The choppers are controlled with current mode, pulse width modulation (PWM) from signals derived from the master module gate driver board. The second set of chopper signals are displaced 60° from the first set of chopper signals in the master module. Together, 30 kW, 40 kW, 50 kW, 75 kW, and 100 kW models have six chopper modules phased 60° apart. The current fed inverter in the slave module uses the same driver signals as the master module.

The slave module’s diagnostic features are coordinated with the master module to provide high performance with virtually any combination of modules. Balance between chopper currents is ensured by independent sampling and feedback control. Power supply, chopper, and inverter modules are synchronized to avoid instabilities at different operating points.