Matrix single-phase power supply voltage regulation technology

Abstract: A matrix single-phase power supply voltage regulation technology is proposed, and its working principle is analyzed, and a safe commutation strategy is given. The simulation results show that the output voltage of this converter is continuously adjustable in a wide range and has a highly sinusoidal input current waveform.

Keywords: single-phase power supply; matrix power conversion; safe commutation strategy

Matrix Single-phase Power Supply Conversion Technique

CAO Yi-long, GONG You-min, YANG Xi-jun, CHEN Bo-shi

Abstract:A matrix single-phase power supply conversion technique is analyzed and a safety current commutation strategy is given. The simulation results show that it can output variable voltage continuously over a wide range and its input current wave is sinuous.

Keywords:Single-phase power supply; Matrix SVR; Safety commutation strategy

Chinese Library Classification Number: TN86 Document Identification Code: A Article Number: 0219-2713(2003)04-0156-04

1 Introduction

The application of single-phase AC power supply is very extensive, such as in rural areas, light industry, household appliances and other small power transmission fields and electric locomotive power supply systems. For single-phase AC power supply, voltage regulation and voltage stabilization are the most common requirements. Currently, there are three types of voltage regulators that can achieve this requirement.

1) Magnetic saturation voltage regulator This voltage regulator adjusts the output voltage by controlling the saturation degree of the inductor in the main circuit to change the reactance value and the voltage on it. This voltage regulator has certain dynamic performance, but the adjustment range of the output voltage is small, and the volume and weight are large.

2) Mechanical voltage regulator Mechanical voltage regulator uses an electric motor to drive carbon brushes to adjust the output voltage. This type of voltage regulator has a better output waveform, but is large in size and weight, and has poor dynamic performance.

3) Electronic voltage regulator This type of voltage regulator is implemented using power electronic devices. Currently, there are two types of voltage regulators: thyristor voltage regulators and inverter voltage regulators. Thyristor voltage regulators use phase control, so their output waveform is poor; inverter voltage regulators use chopper control, and their output waveform and dynamic response are better.

From the above, we can see that the inverter type electronic voltage regulator has the best performance. The structure of the inverter type electronic voltage regulator not only has the ability to regulate and stabilize voltage, but also can realize frequency conversion. It is realized through AC/DC/AC conversion. Its shortcomings are that it has an intermediate DC link - energy storage capacitor and low conversion efficiency. With the development of modern power electronics technology, single-phase power conversion technology has also made great progress. A variety of AC-AC direct conversion schemes using fully controlled devices have emerged. For example, Han-Wood Park et al. proposed a novel high-performance single-phase AC voltage regulator ^[1] ; Douglas Giardini et al. proposed a matrix single-phase buck converter for airport aviation lighting ^[2] ; Zuckerberger et al. proposed a single-phase-single-phase matrix conversion technology with output voltage amplitude modulation and frequency modulation capabilities ^[3] . Based on the matrix conversion theory, this paper proposes a matrix single-phase power conversion circuit. This circuit uses only two bidirectional switching tubes to achieve continuous adjustable output voltage and obtain a high sinusoidal input current waveform.

2 Matrix single-phase power supply voltage regulation principle

The typical topology of single-phase-single-phase matrix power conversion is shown in Figure 1. The input power frequency AC voltage can be converted into a single-phase AC voltage with adjustable amplitude and frequency through a set of switching functions, where S11 _~ S22 _are four bidirectional controllable switches.

Figure 1 Single-phase-single-phase matrix power converter topology

Considering the single-phase power supply as a two-phase power supply, the single-phase-single-phase matrix converter is expected to output two-phase cosine voltages v _o1 ( t ) and v _o2 ( t ), including the output of 0 Hz, where the four-quadrant switches (4QS) S ₁₁ and S ₁₂ are responsible for generating v _o1 ( t ), and S ₂₁ and S ₂₂ are responsible for generating v _o2 ( t ). The output objective function is a two-phase sinusoidal function, and this method can be called the SPWM method.

Let the output objective function be

(1)

Assuming the power supply voltage is _vi ( t ) = Vi sin( ω _it ) _, the expected output voltage is

(2)

In the formula: V _o1 and V _{o2 are the effective values ​​of} vo1 ( t ) and vo2 ( _t ) respectively .

The switching function matrix can be obtained

H=,(3)

Where: h _ij represents the instantaneous duty cycle of the corresponding bidirectional controllable switch, 0≤ h _ij ≤1, i, j =1,2, h ₁₁ ＋ h ₁₂ =1, h ₂₁ ＋ h ₂₂ =1;

Q _o1 and Q _o2 are voltage transformation ratios;

θ ∈[0,2π].

Note that when the input voltage passes through zero, the switching function no longer converges and needs to be processed using the L′hospital law. This control method has the following advantages:

1) Q _o1 and Q _o2 are independently adjustable, so the output voltage range is expanded;

2) The switch utilization rate is greatly enhanced;

3) Methods such as third harmonic injection PWM, switching loss minimum PWM, and switching function-based SVPWM can be directly adopted.

Through the analysis of the above converter topology, the circuit structure can be simplified for single-phase output. The bidirectional switch 4QS-S ₂₂ is short-circuited and 4QS-S ₁₂ is open.

3 Simplified matrix single-phase power regulator

The simplified single-phase power conversion circuit is shown in Figure 2. Its working principle is: use a PWM pulse wave with a fixed duty cycle to drive SB ₁ , apply an equal-width power pulse voltage to the primary side of the transformer, and use the complementary pulse of the above PWM pulse to drive SB ₂ to achieve the primary current of the transformer. As long as the output filter parameters are designed reasonably, a high-sinusoidal output voltage waveform can be obtained, and the higher the switching frequency, the better the effect. The commutation method between SB ₁ and SB ₂ is completed in one step, referred to as the one-step commutation method.

From Figure 2, the difficulty in designing this converter lies in whether the bidirectional controllable switches SB ₁ and SB ₂ can be switched safely. Because the switches are not ideal, there is a possibility of power supply direct connection and transformer primary open circuit when switching between the two, which are both undesirable. Therefore, a safe switching strategy must be adopted when switching between the two.

A four-step commutation method is given below. This is a commutation method determined according to the polarity of the power supply voltage. According to the different polarities of the power supply voltage, a power supply voltage cycle is divided into two sectors. When the power supply voltage is positive, it is defined as sector 1, and when the power supply voltage is negative, it is defined as sector 2.

Figure 2 Simplified single-phase power conversion circuit

1) Switch action rules in sector 1

(1) Preparation

The switch status is Q ₂ and Q ₄ are off, Q ₁ and Q ₃ are off, and the working status is waiting.

(2) Positive half-cycle power supply state

According to the desired switching cycle and duty cycle, Q ₁ and Q ₃ are turned on, and Q ₂ and Q ₄ are turned off, and the working state is power supply.

(3) Switching from power supply state to freewheeling state

Q ₄ is turned on, delay → Q ₁ is turned off, delay → Q ₂ is turned on, delay → Q ₃ is turned off, the working state is freewheeling.

(4) Switching from freewheeling state to power supply state

Q ₃ turns on, delay → Q ₂ turns off, delay → Q ₁ turns on, delay → Q ₄ turns off, the working state is power supply.

2) Switch action rules in sector 2

(1) Preparation

The switch status is Q ₂ and Q ₄ are off, Q ₁ and Q ₃ are off, and the working status is waiting.

(2) Negative half-cycle power supply state

According to the desired switching cycle and duty cycle, Q ₁ and Q ₃ are turned on, and Q ₂ and Q ₄ are turned off, and the working state is power supply.

(3) Switching from power supply state to freewheeling state

Q ₂ turns on, delay → Q ₃ turns off, delay → Q ₄ turns on, delay → Q ₁ turns off, the working state is freewheeling.

(4) Switching from freewheeling state to power supply state

Q ₁ is turned on, delay → Q ₄ is turned off, delay → Q ₃ is turned on, delay → Q ₂ is turned off, the working state is power supply.

Within each sector, this commutation method is safe. It only needs to use the voltage sensor to accurately and quickly detect the polarity of the power supply voltage to determine the sector, without the need for the current sensor to detect the polarity of the primary current of the transformer. Of course, the sensor must have good linearity, rapidity and photoelectric isolation. Since the power supply voltage is very stable, its zero-crossing point detection is relatively accurate and reliable. There is no need to consider switching between sectors, because the switching point only appears at the zero-crossing point of the power supply voltage. When switching, it is only necessary to ensure that there is a path for the primary side of the transformer to continue current. To this end, the following method can be adopted, that is, no matter what state the primary current of the transformer and each switch are in at this time, first turn on Q2 _and Q4 _for continuous current, and after a short delay, turn off Q1 _and Q3 _, and then follow the four-step commutation process.

4 Simulation Results

PSPICE is used to simulate the matrix single-phase power supply regulator with four-step commutation. To enhance the effect, a filter is added to the primary side of the transformer in the simulation circuit, where the inductance is 1mH and the capacitance is 1μF. The primary inductance of the transformer is 100mH, the primary resistance is 2Ω, the secondary side is 100mH, and the voltage ratio is 1. The power supply side filter capacitor is 2μF and the filter inductor is 2mH. The load resistance R _o =5Ω, the output filter capacitor C _o =10μF, and the output filter inductor L _o =20mH. The power supply is a single-phase industrial frequency AC power supply with a switching frequency of 10kHz and an IGBT power switch. Figures 4, 6, 8 and 10 show the transformer output voltage and load current waveforms at duty cycles of 100%, 95%, 50% and 7.5%, and Figures 3, 5, 7 and 9 show the power supply voltage and current waveforms at duty cycles of 100%, 95%, 50% and 7.5%. Simulation shows that the higher the switching frequency, the better the sinusoidal degree of the output voltage and current waveforms; the larger the duty cycle, the higher the output voltage amplitude; the sinusoidal degree of the input current waveform is very high, and there is almost no harmonic current pollution to the power grid.

Figure 3 Power supply voltage and current waveform ( D = 100%)

Figure 4 Transformer output voltage and load current waveform ( D = 100%)

Figure 5 Power supply voltage and current waveform ( D = 95%)

Figure 6 Transformer output voltage and load current waveform ( D = 95%)

Figure 7 Power supply voltage and current waveform ( D = 50%)

Figure 8 Transformer output voltage and load current waveform ( D = 50%)

Figure 9 Power supply voltage and current waveform ( D = 7.5%)

Figure 10 Transformer output voltage and load current waveform ( D = 7.5%)

5 Conclusion

The matrix single-phase power converter proposed in this paper has the characteristics of a small number of switching devices, no need for energy storage capacitors in the middle, continuously adjustable output voltage, and high sinusoidal input current. It is suitable for applications such as constant frequency voltage and speed regulation, UPS, industrial heating, and dimmers. The simulation results verify that the four-step commutation strategy is a safe commutation technology for the matrix single-phase power converter. The matrix single-phase power converter is a product of the combination of power electronics technology and transformer technology. When the switching frequency is very high, the transformer volume and the overall volume can be made very small. This is a promising single-phase power conversion device.