Analysis of the bi-bridge topology and power device circuit of the TPS booster dipole power supply

This study primarily discusses a unique topology for constructing a double full bridge circuit. The study establishes a push-pull inverter model and analyses the balance circuit in its architecture. This allows the power supply to initiate the balance circuit and ensures the TPS (Taiwan Photon Source) booster magnet power supply operates smoothly in a safe and balanced voltage region when magnet energy is recovered. We employ the approach of adding Y circuits to mitigate the impact of common mode (CM) noise. Adding a Y circuit effectively suppresses the common-mode noise generation, improving the quality of the output current of the TPS dipole magnet power supply at low currents state and ramping the beam current energy from 150 MeV to 3 GeV. Furthermore, the reproducibility and stability of the injection point can enhance the injection efficiency of the TPS booster magnet power supply. This study presents the results obtained from these efforts.


Introduction
It has been 8 years since the Taiwan Photon source (TPS) was successfully operated on December 31, 2013.Each subsystem is responsible for the daily maintenance and stable operation of the facility.However, the team focuses on analyzing and researching issues to identify more effective improvement approaches that can reduce damage rates.Our efforts aim to ensure the stability of the light source and improve injection efficiency.The power supply group encounters an issue with the main circuit architecture of the TPS boost ring for the magnet power supply, which requires maintenance work.The main specifications of the power supply are high power and high current, with 1200A/±1800V, and it uses a double full bridge [1] push-pull conversion circuit.The architecture started debugging in 2013 because the original factory only provided a few circuit diagrams and no technical information, which made the team unfamiliar with the circuit topology and load characteristics of the boost power supply.Thus, the system generated a lot of noise, which hindered the smooth injection in the booster ring system.Eventually, a large Y circuit filter was added to the output of the power supply to absorb the generated noise.The Y circuit filter filtered the noise, converting it into current.The noise current be guided back to the ground.Increasing the filter ground current significantly reduces noise flood.Therefore, the power supply can achieve the steady state current required by the injection point.The Y circuit of the XY filter or be named EMI (Electromagnetic interference) line filter [2] shows in figure 1.This study presents a detailed analysis of the real circuit topology of the TPS booster ring dipole magnet power supply, taking advantage of the short maintenance interval of once every two weeks.We established the operating principle used by this power supply.The power supply is a dual full-bridge push-pull converter.We analyze the model of this noise source and establish its noise coupling line path.Typically, current noise is caused by the parasitic capacitance of the high frequency switching of the MOSFETs power device.The modulated pulse wave generated on the circuit can be classified as common mode (CM) noise and differential mode (DM) noise through different paths.The noises can be suppressed using a nonpolar capacitive element and good grounding to form a Y circuit.Noise currents are guided to the ground.

Working principle
The main work principle of the booster dipole magnet power supply is to increase the beam current energy from 150 MeV to 3 GeV.Figure 2 illustrates its working principle.When the beam current reaches 3 GeV, electron beam is extracted from the booster ring and passes to BTS (Booster ring To Storage ring) path section.The beam is guided to the BTS vacuum chamber by the BTS power supply, which provides current to the BTS magnets.Then, the beam enters the storage ring, where it accumulates and stores the electron beam current.The TPS booster dipole magnet power current be dropped from its highest point to the injection point of the magnet for next injection period.The power supply pushes a significant amount of current into the magnet during the time interval from the extract point to the injection point.When the beam current is extracted, the current of the magnet must be guided to the energy storage system of the power supply, which comprises many capacitors called a capacitor bank.This energy is stored in the capacitor bank when the beam current is extracted, and it is used when the booster dipole magnet power supply works in the next injection section.The injection frequency of the TPS booster dipole magnet power works at a frequency of 3 Hz, so we employ sine waves for injection.Figure 3 illustrates the topology of the booster dipole magnet power supply.Since the injection frequency of TPS booster dipole magnet power is a switching mode power supply, the ripple will be higher in low current output compared with high current output.The power supply operates in the two modes: discontinuous current mode (DCM) when working in low current and constant current mode (CCM) when working in high current state.Therefore, when the booster power supply is operating in the injection state, the noise is more significant than when it is operating in the   extraction state.The noise is produced from the topology of the H-bridge, which is the circuit configuration of the booster power.

Topology of the power device
Figure 3 illustrates the circuit configuration of the booster power, which is a push-pull dual active bridge inverter [3].An AC voltage source, Vac, supplies power to two bridge rectifiers, REC1 and REC2, via a dual secondary winding transformer, Tr1, to obtain DC voltage.Voltage-stabilizing capacitors, Ci1 and Ci2, are used to reduce AC ripples.The topology of the Power MOSFETs, S1~S8, forms a full bridge and is controlled by a pulse train generated from sinusoidal pulse width modulation (PWM).The current across nodes A and B, CAB, contains both a high-frequency pulse component and a sinusoidal modulated output current waveform.The high frequency component is screened out by the 2nd-order low-pass filter formed by CF1, LF1, and LF2.In this study, the CM (Common Mode) noise current or grounding current is the current flowing from the common ground node G.The Power MOSFETs S3 and S4 and S5 and S6 is a balanced circuit when beam current is extracted and the energy from the booster magnet returns to the capacitor bank of the booster power supply.The balanced circuit can balance the voltage of Ci1 and Ci2 and keep the voltage within the safety area.
The power devices corresponding to the balanced circuit are S3 to S4 and S5 to S6.Although such a circuit operates in the PWM (Pulse Width Modulation) mode, its circuit is in short circuit mode.Thus, its power devices are susceptible to damage.To address this issue, we must install small inductors to limit the high current produced.However, this is impossible in the actual circuit of the TPS dipole magnet power supply owing to the modularization of the power devices.

Noise of the power supply
Based on the above architecture, the noise of the TPS booster dipole magnet power supply is caused by a bi-full bridge circuit.The real pull-up of current rise and drop is accomplished through an H bridge circuit, as clearly explained in the circuit topology of the power MOSFETs S1~S2 and S7~S8 (refer to Figure 3).Thus, the conduction circuit can provide a clearer explanation of the noise.The conduction noise exists in the form of current flowing inside the circuitry.According to the current flowing path, DM (differential Mode) and CM noises are discussed.Figure 4(a) demonstrates the path of DM noise.DM noise current flows through wires, booster magnets and returns through the same path.The noise path, Vdm, results from high frequency switching actions and proximity electromagnetic coupling in the chokes.However, CM noise current flows through the high and low sides of the power devices.Figure 4(b) provides an example, where the noise source Vcm originates from the high and low side switching of MOSFETs.Nodes A and B experience high frequency pulsating voltage, inducing a high frequency current through ground parasitic capacitance, CP.

Reduce the noise
When analyzing the noise source, it is easy to distinguish between DM noise and CM noise.Since the output to load of the power supply is a large number of booster ring dipole magnets, these magnets naturally form a large inductance, which eliminates the DM noise.However, CM noise cannot be eliminated from the series inductance.
To reduce the CM noise, we add a Y circuit to the output terminal of the power supplier as figure 1, which absorbs the CM noise into the capacitor of the Y circuit and leads it to the ground through the ground wire of the Y circuit.Properly adding a Y circuit to the power supply can achieve the desired output current of the power supply.We can use LISN (Line Impedance Stabilization Network) [4] to check power supply noise.But we have no budget to purchase the LISN for Three-Phase megawatt class instrument.Thus, we can measure the ground current to replace ground voltage ripple from the LISN.The ground current be neutralized after to add Y circuit as figure 5 show the noise current of the without the Y circuit and improved ground wire of the Y circuit.The Inoise be reduced to a small to prove CM noise was greatly reduced.We selected a nonpolarized high quality capacitor with a specific value of 6.2 uF/6kv for the Y circuit.Initially, we employed 5 mm 2 wires for the ground wire of the Y circuit, but it was later realized that it added series inductance, resulting in poor grounding as showed in figure 6 (a).To Adjust the quadrupole magnet power supply family will be increasing the injection efficiency does not require adjusting the booster dipole magnet power supply.
We enhanced the installation of the ground wire by replacing it with a 200 mm 2 braided wire, which effectively guided the noise current to the ground.Figure 6 (b) illustrates the photo of the power supply ground line before and after improvement.Table 1 is showed the improvement of the add Y circuit in TPS booster dipole magnet power supply.

Table 1. The improvement of the add Y circuit
Without the Y circuit With the Y circuit Because the current ripple is too large, the TPS booster dipole magnet power supply cannot boost the energy for the beam current.
The TPS booster dipole magnet power supply can increase the energy of the beam current by reducing the CM noise to make the current ripple smaller.

Conclusion
This study explains the working principle and structure of a booster magnet power supply.The waveform as a current mode inverter that gets the target of the booster dipole magnet employs a waveform generated by an H-bridge.This waveform aligns with the beam current at the injection point of the booster ring, both when the beam current is at 150 MeV and when it is extracted from the booster

Figure 1 .
Figure 1.The Y circuit of the XY filter.

Figure 2 .
Figure 2. Working principle of the TPS booster dipole magnet power supply.

Figure 3 .
Figure 3.The circuit topology of the booster power supply.

Figure 4 .
Figure 4. Differential mode and common mode noises current path.

Figure 5 .
Figure 5.To compare the ground noise current for the without Y Circuit (a) and with the Y Circuit (b) in the booster dipole power supply is output energy to the booster dipole magnets and works at high voltage.

Figure 6 .
Photo of the Y circuit poor grounding wire and the improved ground wire of the Y circuit.