Design and simulation of dual H-bridge bidirectional pulse electroplating power supply

Abstract: In order to make the pulse electroplating power supply output frequency adjustable, voltage adjustable, positive pulse opening time width and negative pulse opening time width adjustable double peak double pulse. A new design scheme that is green, reliable, energy-saving and efficient is proposed. The first H-bridge uses the ZVZCSPWM DC/DC converter to step down the input DC voltage and convert it into a high-frequency AC pulse voltage. Then it is isolated and coupled by a high-frequency transformer, and then a stable DC voltage is obtained through bridge rectification and filtering. Finally, it is switched through the second H-bridge to obtain a double peak bidirectional pulse with any frequency and any duty cycle. Experiments have proved that the application of this scheme can reduce the switching loss of the switch tube, reduce the requirements for components, and increase the efficiency of the power supply to more than 90%. At the same time, since this power supply has a pulse commutation function, it greatly increases the utilization efficiency of precious metals during electroplating.
Keywords: full-bridge phase-shifted soft switch; double H-bridge; double peak bidirectional; PSIM; bidirectional multi-pulse

Since the pulse power supply has a wide range of applications, the development of a high-frequency, efficient, green, reliable, intelligent, and excellent output characteristic pulse power supply has important practical significance for engineering applications. At the same time, the research on pulse power supply involves power electronics, application of new power switching devices, automatic control technology, electromagnetic theory, material science and circuit system modeling, optimization and other aspects, so it has broad theoretical and academic significance. Compared with the traditional charging power supply, the double-peak bidirectional pulse electroplating power supply adopts the power pulse commutation function, which makes the convex parts of the plating layer be strongly dissolved and leveled during electroplating, improves the quality of electroplating, and saves precious metals. It can achieve better electroplating effect and energy saving effect, and has less pollution to the power grid, especially in the electroplating of some special workpieces with precise tolerance requirements, and some occasions where DC power supply electroplating cannot achieve ideal results, such as: connectors and their pins, precision patterns, circuit board vias, microwave circuit boards, multilayer boards, etc. At the same time, the application of new technologies will reduce the pollution of electroplating power supply to the power grid, increase the utilization efficiency of precious metals, reduce enterprise costs, and protect environmental resources.

1 Main circuit structure
The main circuit is shown in Figure 1. The first H-bridge uses a full-bridge phase-shifted soft-switching ZVZCS PWM DC/DC converter to step down the voltage to obtain a high-frequency AC pulse voltage, which is then isolated and stepped down by a high-frequency transformer, and then bridge-rectified and filtered to obtain a stable DC voltage. The bridge-rectified diode here is a fast recovery diode, which can quickly respond to the high-frequency AC pulse coupled from the high-frequency transformer, and an RC absorption network is connected to the fast recovery diode to suppress its parasitic oscillation and reduce the peak voltage. Then the DC voltage obtained by rectification and filtering is sent to the second H-bridge for switching to obtain a double-peak bidirectional pulse of any frequency and any duty cycle. In this circuit, the first H-bridge uses soft switching to avoid the hard switching state of high current and high voltage of the switching device, suppress the inductive turn-off voltage spike and the excessive temperature of the tube when the capacitive is turned on, reduce the switching loss and interference, and reduce the requirements of the switch tube. Through the clever combination of two H-bridges, the efficiency of the power supply is greatly improved, and the cost of power supply production is saved.

2 Working principle and waveform of full-bridge phase-shifted soft-switching converter
In one switching cycle, the full-bridge phase-shifted soft-switching converter has a total of 10 switching modes. Before analysis, the following assumptions are made:
the blocking capacitor Cb is large enough;
is the turns ratio of the primary and secondary windings of the transformer;
all switches and diodes are ideal devices, and capacitors and inductors are ideal components.
1) Switching mode 0 (to moment) At to moment, Vg1 and Vg4 are turned on, and the transformer primary current ip charges the blocking capacitor Cb. The transformer primary side current Ipo=Io/n. The blocking capacitor Cb voltage is UCb(to).
2) Switching mode 1 (to, t1) At to moment, Vg1 is turned off, ip is transferred from Vg1 to C2 and C1, charging C1 and discharging C2. During this period, Llk and L are connected in series, and L is very large. It can be considered that ip is approximately unchanged, similar to a constant current source, and its size is Ipo=Io/n. The transformer primary side current ip continues to charge the blocking capacitor Cb. The voltage of C1 rises linearly from zero, the voltage of C2 drops linearly from Uin, and Vg1 is turned off at zero voltage.

Since Vg1 and Vg4 are turned on at the same time, uAP=0. The secondary diodes of the transformer are turned on at the same time, resulting in zero voltages on the primary and secondary windings of the transformer. Because the leakage inductance is small and the blocking capacitor is large, it can be considered that in this switching mode, the blocking capacitor voltage is basically unchanged, and the primary current is basically linearly reduced, that is,

at t2, the primary current drops to zero, and the duration of this switching mode is

4) Switching mode 3 (t2, t3) Since the diode VD4 blocks the reverse path of ip, the primary current is always zero. This period of time is the recovery time of VD4 and Vg4.
5) Switching mode 4 (t3, t4) At t3, Vg4 is turned off. At this time, no current flows in Vg4, so Vg4 is turned off with zero current. After a very small delay, Vg2 is turned on. Due to the existence of leakage inductance, the primary current cannot change suddenly, and Vg2 is turned on with zero current. Since the primary current is not enough to provide load current, the secondary rectifier tube is still turned on at the same time. The primary and secondary windings of the transformer are clamped at zero voltage. At this time, the voltage applied to the two ends of the leakage inductance is -(Uin+UCbp), and the primary side current increases linearly in the reverse direction from zero. That is,

at t4, the primary side current increases in the reverse direction to the load current. The duration of this switching mode is

6) Switching mode 5 (t4, t5) starts from t4, the primary side provides energy to the load, and at the same time reversely charges the blocking capacitor. The voltage on the blocking capacitor prepares for the next Vg2 zero current shutdown and Vg4 zero current opening. At t5, Vg3 is turned off and another half cycle (t5~t10) begins, and its working conditions are similar to those described above (t0~t5).

3 Technical indicators
Input voltage amplitude Uin=300 V; secondary output voltage Uo=24 V; switch tube operating frequency f=20 kHz; rated output current Io=20 A; output pulse frequency fs=100 Hz; pulse on duty cycle: 17% (i.e. corresponding in PSIM software); pulse off duty cycle: 8% (i.e. corresponding in PSIM software).

4 Circuit component parameter design
1) Selection of switch tube
The maximum voltage that the leading bridge arm can withstand is the maximum DC input voltage Uinmax=300x(1+10%)=330 V. Since the switch tube in this design works in the soft switching state, the maximum voltage stress that the lagging bridge arm can withstand is Uinmax+UCbp=1.2Uinmax=396 V. Since the full-
bridge shift converter switch tube works in the soft switching state, the rated voltage of the power switch tube can be reduced a little, and 500 V can be selected.
The maximum average value of the output filter inductor current is

In this design, the first H-bridge switch tube uses the IRFP450L power MOSFET tube of the HEXFET series of IR company: td(off)=30ns, tf=30 ns, so the switch off time is: toff=tf+td(off)=30+30=60 ns. The second H-bridge switch tube uses the IGBT tube GT40T101. The selection method is similar to the selection of the first H-bridge switch tube, which is not repeated here.
The number of turns of the primary winding of the high-frequency transformer is 118, the number of turns of the secondary winding is 14, and the turns ratio n=8.3.
2) Selection of Llk in the full-bridge shift converter

Combining the above two equations, we get:
26.892 μH 3) Selection of the parallel capacitor Cr (C1, C2) of the leading bridge arm switch tube The role of the buffer capacitor Cr is to achieve the soft switch off of the leading arm. In order to ensure that the leading arm does not pass directly, it must meet

Where fL is the operating frequency of the output filter inductor fL=2f=40 kHz; Ioccm is the nominal minimum current to maintain the continuity of the inductor current. In this design, Ioccm=10%Io is taken; L=44.6μH is obtained. The margin is increased by 10%. In this design, L is taken as 50μH.
6) Selection of output filter capacitor
This design uses 4700 μH tantalum electrolytic capacitors and 4.7 μF ordinary capacitors for parallel filtering.
7) Calculation of each time period of full-bridge shift soft switching

In this design, PISIM simulation software is used, and the PWM module is set by the number of switch points and switch points (expressed in degrees), so the corresponding time must be converted into angles.
PWM1: frequency: 20kHz; number of switching points: 2; switching point: 1.7928 180;
PWM2: frequency: 20kHz; number of switching points: 2; switching point: 181.7928360;
PWM3: frequency: 20 kHz; number of switching points: 2; switching point: 216576.395.13:
PWM4: frequency: 20kHz; number of switching points: 2; switching point: 36.576 215.13;
PWM5: frequency: 100Hz; number of switching points: 4; switching point: 0 60 90 150;
PWM6: frequency: 100Hz: number of switching points = 4; switching point: 180 240 270 330;
PWM7: frequency: 100Hz; number of switching points: 4; switching point: 180 240 270 330;
PWM8: Frequency: 100Hz; Number of switch points: 4; Switching points: 0 60 90 150;

5 Main circuit simulation results
This design uses PSIM as simulation software, which is a simulation software specially designed for power electronics and motor control. It has the advantages of fast simulation function and friendly user interface, and provides a powerful and effective simulation environment for different users. PSIM has the characteristics of unique simulation speed, control of power conversion circuits of any size, and simulation function of control circuits. It is widely used in the simulation field of various systems, design of control loops, and design of motor drive systems. PSIM is used as a simulation tool and design tool, which can greatly improve work efficiency and production performance, and plays a vital role in reducing development costs and shortening the time to factory. The simulation results are shown in Figure 3.

6 Conclusion
1) Nickel plating for non-hole needles: DC plating, 48 hours, plating thickness 240 μm, and rough plating. Using a dual-peak bidirectional pulse plating power supply, the plating thickness of 240 μm only takes 20 hours, the surface is smooth and burr-free. The time saving is nearly 2 times.
2) Double pulse copper plating: When plating copper on PCB boards, the copper layer at both ends of the aperture is usually too thick but the central copper layer is insufficient when using ordinary DC plating, resulting in unqualified printed circuit boards. Now a dual-peak bidirectional pulse plating power supply is used, with a pulse frequency of 1000 Hz, a forward turn-on time of 300 μs, a forward turn-off time of 50 μs, a reverse turn-on time of 100 μs, and a reverse turn-off time of 50 μs, which can overcome the phenomenon of too thick copper layers at both ends of the aperture but insufficient copper layers in the center during DC plating.
The above experiments prove that this scheme can not only improve the quality of electroplating, but also save electroplating time, and has good application value.

Adding 2 times the margin is 6.72 A.
After comprehensive consideration, this design uses the IRFP450LC power MOSFET tube of IR's HEXFET series, VDSS = 500 V, RDS (on) = 0.4 Ω, ID = 14 A, td (off) = 30ns, tf = 30 ns.