Power Quality Control System of High-Power-Density Switching Power Supply for Green Environment

Abstract

There is higher harmonics and electromagnetic interference caused by high-power-density switching power supply during high-frequency and normal operations which affects power quality of switching power supply and also impacts the environment. To solve this problem, this paper proposes a dual digital signal processor (DSP) controller suitable for unified power quality regulators and designs high-power-density switching power supply control system for promoting green environment. The overall structure of the system is divided into two parts, the power main circuit and the control circuit. In the main power circuit, the electromagnetic interference (EMI) filter is used to filter the input AC voltage and convert it into a stable DC voltage. A high-frequency inverter is used to invert the DC voltage into a high-frequency AC voltage to achieve harmonic control and reactive power compensation. In the control circuit, dual DSP controller is used to improve real-time detection, control of the output voltage, and current and driver temperature of the high-power-density switching power supply, while high-precision analysis and processing system collect different information and then achieve the power quality control of the switching power supply based on system software to keep this environment green. The experimental results suggest that the harmonic content of the experimental objects controlled by the system is reduced by 16.7% compared with the existing power quality control and the absolute error of the system is less than 0.02 V which improves the de-noising performance. The power generation systems require that the consumption of natural resources and renewable energy solutions can assist in saving the natural resources.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Switching power supply can greatly improve system reliability and efficiency, so its application is more and more popular [1]. With the gradual maturity of power electronics technology, switching power supply has gradually developed toward high frequency, high efficiency, multi-function, and small size. At the same time, the power capacity and power density of switching power supply also keep rising [2, 3]. As a result, higher harmonics and electromagnetic interference [4] forms in the power grid due to high-frequency on, off, and normal operation of the large power transistor in the switching power supply, which reduces the power quality of the switching power supply.

In [5], the authors proposed a dynamic and directed evaluation model for power quality of distribution network based on the limit interval homogenization method (LIHM). By analyzing the characteristics of power quality data and the way of dynamic information collection, we take into account the margin and heterogeneity of different indexes and homogenize the evaluation data to secure integrity of the evaluation information and fairness of the evaluation. The dynamic evaluation method is introduced for dynamic and directed analysis of power quality of the power distribution system to judge the power quality variation trend of the nodes to be evaluated. Early warnings are given for power quality of each node to provide a reference for further power quality governance strategies, thus achieving comprehensive and objective evaluation of the power quality. A control strategy based on fractional-order sliding mode control to improve the output power quality of permanent magnet synchronous motors is prosed in [6]. The entire control architecture consists of machine-side rectifier control and grid-side inverter control. In the machine-side rectifier control, a fractional-order sliding mode controller is used to control the stator dq-axis current; in the grid-side inverter control, another fractional-order sliding mode controller is used to control the DC link voltage and the grid voltage. At the same time, stability analysis is carried out through the Lyapunov function method and the optimal parameters of the controller are selected. Faster time response and higher tracking accuracy were observed under both steady and variable wind speeds, and there was strong robustness to parameter disturbances. The half-bridge (HB) LLC resonant device with center-tapped secondary side would use the fewest active semiconductor devices among the current DC-DC converter topologies. It attains a wide voltage gain range and continues operating under soft switching conditions across both primary and secondary-side switches. This design makes it suitable for use in in telecom, data center, and battery charging systems [7]. Some researchers have proposed work on self-healing of smart girds during power transmission. Smart sensors, modern ICT tools, and other technologies are used to troubleshoot transmission system issues to prevent environment. A transmission system was developed in [8] equipped with signal processors and communication networks, in order to frequently make decisions and monitor the transmission line parameters. Genetic algorithm (GA) was suggested which was based on optimal voltage control [9]. Unified power flow controller (UPFC) was proposed in [10] to control and analyze the normal power flow. The research described in [10] uses an adaptive synchronous rectifier (SR) system that is deployed on a digital platform to reach a high power density and achieves peak efficiency of more than 90%. To attain a better power density, the research described in [11] uses a matrix transformer; nevertheless, in a severe environment with mechanical vibration, the voltage unbalance across the transformer primary windings presents a problem [12]. As GaN-based switches are used, assortment of secondary-side switches becomes critical.

Because of the conductive interference, harmonic content has become one of the main evaluation criteria for the normal operation of the switching power supply [6–9]. UPQC (unified power quality conditioner) can quickly compensate for sudden rises or dips, fluctuations and flicker in the supply voltage, unbalanced harmonic currents and voltages of each phase voltage, short-term voltage interruptions during faults, etc., which is a power quality controller with comprehensive functions [11, 12]. The performance of UPQC largely depends on the controller level. It uses a fully functional high-speed digital signal processor (DSP) control system to generate PWM wave (pulse width modulation wave), which can simplify the hardware circuit, lower the cost, and improve the system reliability [13, 14]. In view of this, this paper studies dual DSP controllers suitable for UPQC and designs high-power-density switching power supply control system, so that high-power-density switching power supply can have better power quality.

1.1. Research Key Highlights

(i) This paper proposes a dual DSP controller suitable for unified power quality regulators and designs high-power-density switching power supply control system for promoting green environment.

(ii) The overall structure of the system is divided into two parts, the power main circuit and the control circuit.

(iii) In the main power circuit, the EMI filter is used to filter the input AC voltage and convert it into a stable DC voltage. A high-frequency inverter is used to invert the DC voltage into a high-frequency AC voltage to achieve harmonic control and reactive power compensation.

(iv) In the control circuit, dual DSP controller is used to improve real-time detection, control of the output voltage, and current and driver temperature of the high-power-density switching power supply, while high-precision analysis and processing system collect different information and then achieve the power quality control of the switching power supply based on system software to keep this environment green.

(v) The experimental results suggest that the harmonic content of the experimental objects controlled by the system is reduced by 16.7% compared with the existing power quality control and the absolute error of the system is less than 0.02 V which improves the de-noising performance. For comparison analysis, a signal’s expected level of signal-to-background noise (SNR) and the ratio of a signal’s maximum power value to the power of the noise that distorts it (PSNR) are utilized.

(vi) The innovative switching control techniques can save energy and help to retain the environment green by reducing carbon footprints.

The rest of the paper is organized as follows: In section 3, the power control system design is elaborated. In section 4, the results obtained from the proposed method are analysed. Section 5 summarizes the proposed work.

2. Power Quality Control System Design for Switching Power Supply

2.1. The Overall System Structure

The power quality control system structure of high-power-density switching power supply is mainly divided into two parts, power main circuit and control circuit, as shown in Figure 1.

[figure(s) omitted; refer to PDF]

It can be seen from Figure 1 that the main power circuit includes an EMI (electromagnetic interference) filter and a high-frequency transformer. The control circuit includes a DSP controller, a drive module, a protection module, an auxiliary module, and a sampling module. In the main power circuit, the EMI filter filters the input AC voltage and converts it into stable DC voltage. Using a high-frequency inverter, it inverts the DC voltage into high-frequency AC voltage for harmonic control and reactive power compensation. In the control circuit, the DSP controller is used to detect and control the output voltage, and current and driver temperature of the high-power-density switching power supply in real time, and analyze and process the different information collected by the system. It then implements power quality control of the switching power supply using system software.

2.2. Filter Design

The low-pass filter circuit constructed by the series reactor and the parallel capacitor, namely, EMI filter [15, 16], suppresses the interference of higher harmonics through the common mode choke, thus improving the power quality of the switching power supply. The main purpose of setting EMI filter at the input end of the system power supply is to avoid common mode and differential mode interference signals with high-power-density switching power supply in the power line which will affect other equipment or devices. Moreover, it can also reduce the noise generated inside high-power-density switching power supply. Figure 2 describes the circuit structure of the EMI filter, where $C_X$, $C_Y$, and $L$ represent differential mode capacitor, common mode capacitor, and common mode choke, respectively [17].

[figure(s) omitted; refer to PDF]

A common mode choke, which consists of two indifferent coils wound in the same direction over a magnetic core, is used in EMI filters to decrease common mode interference signals. When the common mode interference signal current passes by, the two coils in the common mode choke have the same magnetic flux direction and reinforce each other, so that the inductance value of each coil redoubles to strongly and effectively suppress the common mode interference signal. Based on the above principles, the EMI filter is used to filter the input AC voltage, remove the interference signal, and convert it into stable DC voltage.

2.3. Design of High-Frequency Inverter

By converting the DC voltage output by the EMI filter via a high-frequency inverter, the DC voltage is inverted into high-frequency AC voltage for harmonic control and reactive power compensation. Its working principle is as follows:

When the power transmission system is in resonance, the input impedance of the switching power supply exhibits purely resistive characteristics and the input current is in phase with the voltage. At this time, the power factor of the power transmission system is 1, the output useful work reaches the maximum, and the harmonics are greatly increased. The circuit structure of the high-frequency inverter is shown in Figure 3.

[figure(s) omitted; refer to PDF]

In Figure 3, the driving signal adjustment power switch tube is described by four parameters $Q_1$, $Q_2$, $Q_3$, and $Q_4$, respectively. The two switch tubes on the diagonal line are turned on at the same time; that is, $Q_1$ and $Q_2$ are turned on at the same time, and $Q_3$ and $Q_4$ are turned on at the same time. This working mode causes the voltage on the load to be reversed. By changing the on-time of the switch tube, the DC voltage is inverted into high-frequency AC voltage to achieve the inversion, where the inductance $L$ can be used as the primary coil of the high-frequency inverter, and the capacitor $C$ is not only a part of the EMI filter circuit, but also the series compensation capacitor of the primary coil of the high-frequency inverter, thus achieving voltage harmonic control and reactive power compensation.

2.4. DSP Control Module Design

The essence of DSP control is digital control. Using DSP to control the switching power supply, through the digital signal processor, stable output voltage and output current are possible. Digital signal processing system is based on digital signal processing, so it possesses all the advantages of digital processing [18, 19].

(1) Good Stability. The DSP system is based on digital processing, which is less affected by ambient temperature and noise and has high reliability.

(2) High Precision. The 16-bit digital system can reach 510− precision.

(3) Good Repeatability. The performance of the analog system is greatly affected by the performance changes of the component parameters, while the digital system is basically unaffected. Therefore, the digital system facilitates testing, debugging, and mass production.

(4) Convenient Integration. The digital components in the DSP system are highly standardized, which facilitates large-scale integration.

The CPU of the TMS320F240 digital signal processor is a DSP core with 16 fixed points, which has good portability. The calculation function is up to 25MIPs, the data bus and the address bus are independent, and the high-quality calculation function can guarantee complex and real-time control of the system. TMS320C3X is TI’s third-generation product and also the first-generation floating-point DSP chip. TMS320C3X currently has three types: TMS320C30, TMS320C31, and TMS320C32. TMS320C32 is a simplified and improved simplification of TMS320C31. The main purpose is to reduce the internal RAM from 2K words to 512 words to reduce costs. Improvements include variable external memory width and relocation of the interrupt vector table, and level trigger or edge trigger can be selected for external interrupts by software. DMA controller is added with a channel. In addition, two power-saving operation modes are added and HOLD function and JTAG emulation function are supported. Figure 4 illustrates the structure diagram of TMS320F240 digital signal processor.

[figure(s) omitted; refer to PDF]

Based on the characteristics of the two chips selected above, the schematic diagram of the unified power quality dual DSP controller system is shown in Figure 5.

[figure(s) omitted; refer to PDF]

The whole system can be divided into algorithm module, input and output control module, dual-computer communication module, logic coordination module, and data acquisition module.

(1) The algorithm module executed by TMS320C32 is the calculation center of the entire system, which completes data analysis and calculation. It generates the harmonic compensation command current.

(2) The input and output control module takes TMS320F240 as the center, which is responsible for the collection and processing of system data, the actuator control and drive in the external system, and the man-machine interface functions.

(3) The communication between the two computers is completed by the dual-port RAM of IDT Company, which is responsible for the maintaining public data exchange DSP in a parallel working state. The reason why the dual-port RAM is selected is that such communication mode has a high data transmission rate and good anti-interference performance.

(4) The logic coordination module is executed by the programmable logic device XC95108 of XINLINX Company, which implements the control logic required by the entire system and extends the various switching values required by the system to reserve a certain margin for the system expansion. The use of CPLD simplifies the entire system design and contributes to system confidentiality and flexibility.

(5) The data acquisition system is composed of two major parts, and the arithmetic signals required by the system are processed by the MAX125 chip of MAXIM Company. The protection signal acquisition for the main circuit is done by F240. For this reason, although the F240 chip contains dual 10-bit analog-to-digital conversion modules, there are only 16 input channels in total, and only two inputs can be sampled and converted at the same time. Moreover, its conversion time is 6.6 microseconds, which cannot meet the requirements for simultaneous sampling of multiple input signals and power parameter accuracy in power parameter measurement. MAX125ADC is a 14-bit A/D converter with multiple-way switch and sampling/protection circuit. With 8 conversion modes and a power-saving mode, it enables users to choose between 2 sets of multiple-way switches and 4 input channels that are sampled at the same time, so that it is easy to ensure the correct phase relationship between the sampled three-phase power frequency signals.

The function of this system is executed by TMS320F240. The PWM signal is generated by the FULLCOMPARE/PWM unit of TMS320F240. It has six output terminals, mainly involving three registers: period register, comparand register, and count register. The period register determines the PWM signal period, and the output of the PWM signal is set to 1 or 0 at the beginning of each period (can be set in software). In a cycle, the value of the count register increases by 1 every time a machine clock cycle passes which is then compared with the value of the comparand register. If the two are equal, the output of the PWM unit will flip. Otherwise, it will remain unchanged. When the value of the counter register is equal to that of the period register, the counter register is reset to 0 to re-count and start the next cycle. Then, the PWM output with different values written into the comparand register in different cycles will have different duty cycles, as shown in Figure 6.

[figure(s) omitted; refer to PDF]

The system is controlled in real time through the control program of the DSP control module in the control circuit, and the average value of the sampling parameters is calculated to secure the highest sampling accuracy. To enhance the system implementation, the programming ideas of time sharing and task priority control are used in the main loop of DSP control to ensure high-quality human-computer interaction functions and real-time control operations [20]. The main program flowchart of DSP control is shown in Figure 7.

[figure(s) omitted; refer to PDF]

The main program of power quality control system of high-power-density switching power supply starts the main loop after initializing the system clock configuration, interrupt vector table setting, sampling module, event manager, etc., in the initial stage of operation. It controls sampling module and event manager through interrupt control mode. The sampling module collects signals such as system differential mode capacitance and common mode capacitance duty cycle acquired after one-cycle control of the EMI filter. The purpose of A/D converter and the event manager interrupt is to select the sampling channel and start a new round of sampling at the same time. Meanwhile, filtering is performed on the sampled signal, and the duty cycle value of the new cycle is selected by evaluating the duty cycle change flag variable. The key management, serial communication management, LCD management, alarm management, and PI calculation of sampling data are completed in the main loop controlled by DSP.

2.5. System Software Design

Based on indicators such as voltage, reactive power, electromagnetic interference, current fluctuations, and harmonic distortion rate, EMI filters and high-frequency inverters are used as control variables to construct a power quality control objective function of switching power supply. Reliability of the switching power supply is calculated as given in$$\begin{array}{}\text{(1)}& T={\displaystyle \int gx>0}fxdx.\end{array}$$

In (1), $fx$ represents the joint probability density function, $gx$ is the state function of the switching power supply, $gx<0$ represents low control stability, $gx>0$ represents high control stability, and switching power supply has high reliability in this state. $gx=0$ indicates that the switching power supply is in a state of extreme load, and when the random vector $x$ obeys normal distribution, the first-order estimator of reliability of the switching power supply is expressed in$$\begin{array}{}\text{(2)}& z\alpha =z\frac{u_g}{{\omega }_g}=z\frac{Egx}{\sqrt{Dgx}},\end{array}$$where $z\alpha$ is the normal distribution function, $\alpha$ represents the reliability evaluation index of the switching power supply, and $u_g$ and ${\omega }_g$, respectively, represent the standard deviation and the mean value of the switching power supply state function.

According to the above analysis, the power quality control model of the switching power supply is constructed as shown in [16]$$\begin{array}{}\text{(3)}& \begin{array}{c}\min fx=w_1{f}_{1}x+w_2{f}_{2}x+w_3{f}_{3}x+w_4{f}_{4}x,\\ s.t.W_{a\min }\le W_a\le W_{\text{max}},\\ s.t.0\le Q_c\le Q_{c\max },\\ s.t.0\le {\lambda }_{bci}\le {\lambda }_{b{c}_{\max }},\end{array}\end{array}$$where $w_1,w_2,w_3,w_4$ are the weighting factors of voltage, reactive power, electromagnetic interference, and current fluctuations, $f_{1}x$ is the switching power supply voltage volatility index, $f_{2}x$ is the reactive power volatility index, $f_{3}x$ is the electromagnetic interference index, $f_{4}x$ is the current fluctuation index, and $Q_c$ is reactive power output of the EMI filter, high-frequency inverter, and ${\lambda }_{b{c}_i}$ represents the harmonic distortion rate.

Experiment is carried using the above-discussed power quality control system, and the results are discussed in Section 3.

3. Experimental Analysis

3.1. Control Effect Comparison

The experiment takes high-power-density switching power supply of a certain model as the experimental object and compares the voltage waveform and output current harmonics at the output end of the experimental object without power quality control and those with the system control in this paper. The load as well as other variables is the same before and after the power quality control, and the results are shown in Figures 8 and 9.

[figure(s) omitted; refer to PDF]

Analysis of Figures 8 and 9 shows that without power quality control, the harmonic content in the input current waveform of the experimental object is approximately 19% [16], and when the system herein is used for power quality control, the highest harmonic content at the input current waveform of the experimental object is only about 1.4%, which is 17.6% lower than that without power quality control. The experimental results show that the system herein can effectively control the power quality of high-power-density switching power supply.

3.2. Comparison of Control Accuracy

Set the control reference value of the experimental object to 0.56 V, 2.77 V, 5.50 V, 10.36 V, 20.22 V, and 30.85 V, and use different control systems to control the experimental object. After 5 minutes, measure the voltage of the experimental object under the control of different systems, and compare the absolute errors of different control systems to verify the control accuracy of the system herein. The results are shown in Table 1.

Table 1

Control accuracy comparison results of different systems.

Serial number	Measured voltage (V)
	Set voltage (V)	Of the system herein	Absolute error (V)
1	0.56	0.56	0
2	2.77	2.77	0
3	5.50	5.50	0
4	10.36	10.36	0
5	20.22	20.20	0.02
6	30.85	30.86	-0.01
		Control system based on limit interval homogenization
1	0.56	0.56	0
2	2.77	2.77	0
3	5.50	5.50	0
4	10.36	10.33	0.03
5	20.22	20.18	0.04
6	30.85	30.78	0.07
		Power quality control system of permanent magnet synchronous motor
1	0.56	0.56	0
2	2.77	2.77	0
3	5.50	5.50	0
4	10.36	10.38	-0.02
5	20.22	20.18	0.04
6	30.85	30.88	0.03

It can be seen from Table 1 that when the system herein controls the experimental object, the control reference value is higher than 20V. There will be control error, and the absolute error is within 0.02 V. When the other two control systems control the experimental object and if the control reference value is higher than 10V, there will be control error, where the absolute error of the control system based on limit interval homogenization gradually increases with the increase of the reference control variable, while the absolute error of quality control system of the permanent magnet synchronous motor power is controlled within 0.04 V. By contrast, it can be seen that the system herein has higher control accuracy than the comparison system.

3.3. Comparison of Control Response Time

Different control systems are used to control the power quality of the experimental objects. The power quality expected to be achieved after the control is described by 100%, and the measurement is performed once every 2s. The response time of different control systems in power quality control of the experimental objects is compared. The results are shown in Table 2.

Table 2

Comparison of control response time of different systems.

System herein		Control system based on the limit interval homogenization		Power quality control system of permanent magnet synchronous motor
Measurement time (s)	Power quality (%)	Measurement time (s)	Power quality (%)	Measurement time (s)	Power quality (%)
2	96.84	2	90.58	2	93.68
4	99.27	4	94.66	4	95.74
6	100	6	98.07	6	98.26
8	100	8	99.32	8	100
10	100	10	99.69	10	100
12	100	12	98.16	12	99.71
14	100	14	99.33	14	98.59
16	100	16	99.82	16	99.40
18	100	18	98.75	18	99.29
20	100	20	99.40	20	100
22	100	22	100	22	99.71
24	100	24	100	24	100
26	100	26	100	26	100
28	100	28	100	28	99.09
30	100	30	100	30	99.83

Analysis of Table 2 shows that under the system control proposed in this paper, the power quality of the experimental object reaches 100% in the 6th second, which always maintains at 100% in the following 24 s. Under the system control based on limit interval homogenization, the power quality of the experimental object reaches 100% in the 22nd second, which always maintains at 100% in the subsequent 8 s. Under the power quality control system control of the permanent magnet synchronous motor, the power quality of the experimental object reaches 100% in the 8th second, but fluctuates in the subsequent 22 s. By contrast, the system proposed in this paper has the fastest power quality control response and the most stable control effect.

3.4. Comparison of De-Noising Performance

The experiment is to test the de-noising performance of the system in this paper. Under the same experimental environment, the effects of the three control systems in eliminating noise were tested and compared. The noise types are mainly divided into Gaussian noise and salt and pepper noise. The comparison results are shown in Tables 3 and 4. Figure 10 represents PSNR of different systems under Gaussian noise (dB).

Table 3

Peak signal-to-noise ratio of different systems under Gaussian noise (dB).

	SNR/dB	PSNR/dB
Proposed system	11.35	27.89
Control system based on limit interval homogenization	9.88	23.89
Power quality control system control of the permanent magnet synchronous motor	10.51	21.33

Table 4

Peak signal-to-noise ratio of different systems under salt and pepper noise (dB).

	SNR/dB	PSNR/dB
Proposed system	17.94	34.27
Control system based on limit interval homogenization	8.18	25.24
Power quality control system control of the permanent magnet synchronous motor	10.49	27.27

[figure(s) omitted; refer to PDF]

The analysis of Tables 3 and 4 reveals that the signal-to-noise ratio (SNR) and peak signal-to-noise ratio (PSNR) of the system used in this study are 11.35 dB and 27.89 dB, respectively. These values are greater than those of the other two systems by at least 0.84 dB and 6.56 dB. Regarding the comparison results of salt and pepper noise elimination, the signal-to-noise ratio (SNR) and peak signal-to-noise ratio (PSNR) of this system are, respectively, 17.94 dB and 34.27 dB, which are higher than that of the other two systems by 7.45 dB and 7.00 dB or more. The comparison results as shown in Figures 10 and11 indicate that the proposed system has superior de-noising performance than the comparison system when it is used to control the power quality of high-power-density switching power supply.

[figure(s) omitted; refer to PDF]

4. Conclusion

With the popularization of high-power-density switching power supply applications, the power quality control has become a hot topic to save energy and to protect environment by saving energy. This paper designs a high-power-density switching power supply control system with dual DSP controllers and prevents complex harmonics, and reactive current calculations in high-power-density switching power supply using single-cycle control algorithm in the EMI filter are suggested. This research article is implementing power quality control of high-power-density switching power supply for saving energy and promoting green environment. The experimental results show the proposed research is effectively controlling the power quality of high-power-density switching power supply and saving the energy. In the comparative results of peak signal-to-noise ratio of different systems under Gaussian noise (dB) and under salt and pepper noise, the noise elimination of the proposed system is 0.84 dB and 6.56 dB, respectively, and the SNR is more than 7.45 dB and 7.00 dB, respectively. The system in this paper has the advantages of high control accuracy, fast response, and good de-noising performance which helps to save energy and to keep the environment green. As a future improvement to this research work, software and communication technologies can be used to measure high-power-density switching power supply approaches.

Acknowledgments

The research work has received resources from Sichuan Science and Technology's projects on Research and development of intelligent manufacturing cell for PCB forming (2021YFG0189) and Achievement transformation of PCB six axis drilling and milling high speed numerical control unit (2021ZHCG0015).

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