A Unified Control Method for Power Factor Correction of Single-Phase DCM Boost Converter

Abstract

A unified control method for power factor correction of a single-phase DCM Boost converter comprises: constructing a converter topology with virtual elements based on a topology of a Boost PFC converter; performing switch average modeling on the constructed converter topology; deriving a calculation formula for a switching frequency and a duty cycle under a unit power factor achieved by the converter topology, and calculating a switching period and a conduction time by using the derived calculation formula; introducing control parameters and designing the voltage of the virtual elements to unify pulse width modulation control and pulse frequency modulation control; changing the control parameters according to the load condition of the converter to select a corresponding converter control method to control the system; making full use of two control degrees of freedom to unify the pulse width modulation control and the pulse frequency modulation control, so that the converter can operate efficiently under different load powers.

Description

Technical Field

[0001] The invention relates to the fields of power electronic current conversion technology and control technology, and in particular to a unified control method for power factor correction of a single-phase DCM Boost converter. Background Art

[0002] The existing DCM Boost PFC control methods are mainly divided into pulse frequency modulation control and pulse width modulation control. The main idea of ​​pulse frequency modulation control is to keep the on-time or off-time of the switch constant, that is, to adjust the output voltage by changing the switching frequency. It mainly includes constant on-time, constant off-time or fixed off-time and hysteresis control. Compared with pulse frequency modulation control, pulse width modulation control has received more attention due to its relatively simple input filter design. By adjusting the duty cycle in real time, sinusoidal grid current and unity power factor are achieved.

[0003] As early as the 1990s, pulse width modulation strategies were applied to Boost PFC converters to improve the quality of grid current. The expression of the duty cycle is based on the assumption that the average inductor current in the switching cycle is proportional to the grid voltage. However, the calculation of the duty cycle contains square roots, which takes up a lot of resources of the digital processor. Limited by the performance of early digital processors, some scholars developed analog circuits to control Boost PFC converters. And in order to simplify the circuit implementation, the duty cycle was further approximated. Other scholars further simplified the control circuit by injecting the third harmonic (in phase with the fundamental current) into the input current. At the same time, the peak current and the root mean square current are reduced. Therefore, the size of the DC filter capacitor can be reduced. Both of the above methods use analog circuits to achieve control. Unlike the above-mentioned analog circuits, some scholars have proposed a pulse train control strategy to simplify the control logic. It does not depend on the operating speed of the digital processor, so it does not require an expensive high-speed digital processor.

[0004] As we all know, active switches have two control degrees of freedom: duty cycle and switching frequency. However, the above control methods only use one degree of freedom, and currently few scholars use both degrees of freedom in one control method. If these two degrees of freedom can be fully utilized, the control of the converter can be further optimized, so that it can cope with a variety of power conditions, making the use of DCM Boost PFC converters more extensive. Summary of the invention

[0005] The present invention provides a unified control method for power factor correction of a single-phase DCM Boost converter, the purpose of which is to make full use of two control degrees of freedom in a set of control of the DCM Boost converter, unify the pulse width modulation control and the pulse frequency modulation control, so that the converter can operate efficiently under different load powers.

[0006] In order to achieve the above object, the present invention provides a unified control method for power factor correction of a single-phase DCM Boost converter, comprising:

[0007] Step 1, constructing a converter topology with virtual components based on the topology of the Boost PFC converter;

[0008] Step 2, performing switch average modeling on the constructed converter topology;

[0009] Step 3, deriving a calculation formula for the switching frequency and duty cycle of the converter topology structure under unity power factor, and calculating the switching period and the on-time by using the derived calculation formula;

[0010] Step 4, introduce control parameters and design the voltage of the virtual element to unify the pulse width modulation control and the pulse frequency modulation control;

[0011] Step 5: According to the load condition of the converter, change the control parameters and select the corresponding converter control method to control the system.

[0012] The virtual components are a virtual power supply and a virtual inductor. The virtual power supply and the virtual inductor are connected in series and then in parallel to the freewheeling diode at the output end of the Boost PFC converter, forming a converter topology with a virtual power supply and a virtual inductor.

[0013] Among them, the switch average model in step 2 is

[0014]

[0015] Among them, L 1 Is the main circuit inductance, L 2 is the virtual inductance value, v r is the rectified input voltage, v dc is the converter output voltage, v a is the voltage value of the virtual voltage source, d 1 ,d 2 is the proportion of the switching cycle.

[0016] The specific derivation process in step 3 includes:

[0017] According to the balanced characteristics of the inductor, the average switching model of the inductor current can be obtained:

[0018] v r d 1 T s +(v r -v dc )d 2 T s =0

[0019] Among them, T s is the switching period, and the duty cycle d is calculated according to the above formula 1 With d 2 The relationship is:

[0020]

[0021] According to the switch average concept, the inductance L can be obtained 1 The average switching current expression is:

[0022]

[0023] Among them, i pk is the inductance L 1 The peak value of the current meets the following conditions:

[0024]

[0025] According to the above formula, the inductance L can be calculated 1 The average switching current is:

[0026]

[0027] According to the power conservation law, we know that the grid-side input power i g v g The rectified input power i 1ave Equal, so combined with the above formula, the expression of switching frequency can be calculated as:

[0028]

[0029] The duty cycle d is calculated based on the average model of the inductor current switch 1 for:

[0030]

[0031] Substituting the above formula into the switching frequency expression, the further switching frequency is calculated as:

[0032]

[0033] According to the duty cycle d 1 And the formula of switching frequency can calculate the on-time of the switch as:

[0034] Wherein, step 4 comprises:

[0035] Assume that the introduced control parameter is A, and the designed virtual voltage source voltage is:

[0036]

[0037] According to the calculation formula of duty cycle and switching frequency, the duty cycle d 1 and the switching frequency f s It can be expressed as:

[0038]

[0039] When A=0, At this time, the switching frequency is variable and the duty cycle is fixed, which is pulse frequency modulation control;

[0040] when hour, At this time, the switching frequency is fixed and the duty cycle is variable, which is pulse width modulation control;

[0041] when When , both the switching frequency and the duty cycle are changing, and both types of control exist.

[0042] Among them, step 5 specifically determines the working state of the converter as follows:

[0043] When the converter works under light load, the control mode is switched to pulse width modulation control; when the converter works under heavy load, the control mode is switched to pulse frequency modulation control.

[0044] The above technical solution of the present invention has the following beneficial effects:

[0045] The present invention makes full use of two control degrees of freedom in a set of control, unifies pulse width modulation control and pulse frequency modulation control, and enables the converter to maintain high-efficiency operation under different load powers by switching one control parameter.

[0046] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the process of the present invention;

[0048] Figure 2 The schematic diagram of the DCM Boost PFC converter with virtual components;

[0049] Figure 3 Schematic diagram of the inductor current of the main circuit;

[0050] Figure 4 is the circuit schematic diagram of the proposed control method;

[0051] Figure 5 The experimental waveform diagram of the pulse width modulation control in the present invention applied to the DCM Boost PFC circuit with heavy load and light load;

[0052] Figure 6 The experimental waveform diagram of the pulse frequency modulation control in the present invention applied to the DCM Boost PFC circuit with heavy load and light load;

[0053] Figure 7 This is an efficiency diagram of the present invention applied to a DCM Boost PFC circuit. DETAILED DESCRIPTION

[0054] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0056] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a locking connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0057] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] like Figure 1A unified control method for power factor correction of a single-phase DCM Boost converter is shown, comprising:

[0059] Step 1, constructing a converter topology with virtual components based on the topology of the Boost PFC converter;

[0060] Step 2, performing switch average modeling on the constructed converter topology;

[0061] Step 3, deriving a calculation formula for the switching frequency and duty cycle of the converter topology structure under unity power factor, and calculating the switching period and the on-time by using the derived calculation formula;

[0062] Step 4, introduce control parameters and design the voltage of the virtual element to unify the pulse width modulation control and the pulse frequency modulation control;

[0063] Step 5: According to the load condition of the converter, change the control parameters and select the corresponding converter control method to control the system.

[0064] Among them, the virtual components are virtual power supply and virtual inductor. The virtual power supply and virtual inductor are connected in series and then connected in parallel to the freewheeling diode at the output end of the Boost PFC converter, forming a converter topology with virtual power supply and virtual inductor, such as Figure 2 shown.

[0065] Specifically, according to the converter operating characteristics, a switching cycle in step 2 can be divided into three stages: the switch on stage; the switch off stage to the stage from when the inductor current i L1 decreases to 0; and the remaining time stage. Figure 3 The diagram shows the change of inductor current in these three stages.

[0066] Phase 1: Differential equation of the main circuit inductor current:

[0067]

[0068] Among them, L 1 Is the main circuit inductance, L 2 is the virtual inductance value, v r is the rectified input voltage, v dc is the converter output voltage, v a is the voltage value of the virtual voltage source.

[0069] Phase 2: Differential equation of the main circuit inductor current:

[0070]

[0071] Stage 3: Differential equation of the inductor current in the main circuit:

[0072]

[0073] Combining the above three stages, the switch average model is derived as follows:

[0074]

[0075] Among them, L 1 Is the main circuit inductance, L 2 is the virtual inductance value, v r is the rectified input voltage, v dc is the converter output voltage, v a is the voltage value of the virtual voltage source, d 1 ,d 2 is the proportion of the switching cycle.

[0076] The specific derivation process in step 3 is as follows:

[0077] according to Figure 3 As shown in the figure, the balanced characteristics of the inductor can be obtained from the switching average model of the inductor current:

[0078] v r d 1 T s +(v r -v dc )d 2 T s =0 (5)

[0079] Among them, T s is the switching period, and the duty cycle d is calculated according to the above formula 1 With d 2 The relationship is:

[0080]

[0081] According to the switch average concept, the inductance L can be obtained 1 The average switching current expression is:

[0082]

[0083] Among them, i pk is the inductance L 1 The peak value of the current meets the following conditions:

[0084]

[0085] According to the above formula, the inductance L can be calculated 1 The average switching current is:

[0086]

[0087] According to the power conservation law, we know that the grid-side input power i g v g The rectified input power i 1ave Equal, so combined with the above formula, the expression of switching frequency can be calculated as:

[0088]

[0089] The duty cycle d is calculated based on the average model of the inductor current switch 1 for:

[0090]

[0091] Substituting the above formula (11) into the switching frequency expression, the further switching frequency is calculated as:

[0092]

[0093] According to the duty cycle d 1 And the formula of switching frequency can calculate the on-time of the switch as:

[0094] Wherein, step 4 comprises:

[0095] Assume that the introduced control parameter is A, and the designed virtual voltage source voltage is:

[0096]

[0097] According to the calculation formula of duty cycle and switching frequency, the duty cycle d 1 and the switching frequency f s It can be expressed as:

[0098]

[0099] The relationship between the value of control parameter A and the duty cycle and switching frequency is shown in Table 1:

[0100]

[0101] It can be seen from the above table (1) that when A = 0, At this time, the switching frequency is variable and the duty cycle is fixed, which is pulse frequency modulation control;

[0102] when hour, At this time, the switching frequency is fixed and the duty cycle is variable, which is pulse width modulation control;

[0103] when When , both the switching frequency and the duty cycle are changing, and both types of control exist.

[0104] The specific working state of the converter in step 5 is as follows:

[0105] When the converter works under light load, the control mode is switched to pulse width modulation control; when the converter works under heavy load, the control mode is switched to pulse frequency modulation control.

[0106] According to step 4, after determining the control method, the control method is combined with the DCM Boost PFC circuit, and the control scheme can be designed as follows Figure 4 As shown, the method of the present invention is in accordance with Figure 2 The waveforms obtained by testing the circuit shown in the figure under heavy load and light load are as follows: Figure 5 , Figure 6 The specific experimental parameters are shown in Table 2:

[0107]

[0108] The above algorithm is implemented using DSP and Figure 2 The DCM Boost PFC converter shown in the figure is controlled. The converter input current waveform is good in steady state, which meets the IEC61000 standard, and the output voltage has a good steady-state tracking effect, and the input PF value reaches 0.998. In order to make the converter still operate at a higher efficiency under a wider load condition, when the converter works in light load mode, pulse width modulation control should be selected, and when the converter works in heavy load mode, pulse frequency modulation control should be selected. Figure 7 A comparison of converter efficiency between the two control modes under different load powers is given.

[0109] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A unified control method for power factor correction of a single-phase DCM Boost converter, characterized in that: include: Step 1, constructing a converter topology structure with virtual components based on the topology structure of the Boost PFC converter, wherein the virtual components are a virtual power supply and a virtual inductor; Step 2, performing switch average modeling on the constructed converter topology, including: According to the working characteristics of the converter, a switching cycle can be divided into three stages. Based on the differential equations of the three stages, the constructed converter topology is modeled by switching average to obtain a switching average model. Step 3, deriving a calculation formula for the switching frequency and duty cycle of the converter topology structure under unity power factor, and calculating the switching period and the on-time by using the derived calculation formula; Step 4, introduce control parameters and design the voltage of the virtual element to unify the pulse width modulation control and the pulse frequency modulation control, including: Assume that the introduced control parameter is A, and the designed virtual voltage source voltage is: According to the calculation formula of duty cycle and switching frequency, duty cycle d1 and switching frequency f s It can be expressed as: When A=0, At this time, the switching frequency is variable and the duty cycle is fixed, which is pulse frequency modulation control; when hour, At this time, the switching frequency is fixed and the duty cycle is variable, which is pulse width modulation control; when When , the switching frequency and duty cycle are both changing, and both types of control exist; Step 5: According to the load condition of the converter, change the control parameters and select the corresponding converter control method to control the system.

2. The unified control method for power factor correction of a single-phase DCM Boost converter according to claim 1, characterized in that: The virtual power supply and the virtual inductor are connected in series and then connected in parallel to the freewheeling diode at the output end of the Boost PFC converter, forming a converter topology structure with a virtual power supply and a virtual inductor.

3. The unified control method for power factor correction of a single-phase DCM Boost converter according to claim 1, characterized in that: The switch average model described in step 2 is Among them, L1 is the main circuit inductance value, L2 is the virtual inductance value, v r is the rectified input voltage, v dc is the converter output voltage, v a is the voltage value of the virtual voltage source, d1 and d2 are the proportions of the switching cycle.

4. The unified control method for power factor correction of a single-phase DCM Boost converter according to claim 3, characterized in that: The step 3 specifically includes: According to the balanced characteristics of the inductor, the switch average model of the inductor current can be obtained: v r d1T s +(v r -v dc )d2T s =0 Among them, T s is the switching period. According to the above formula, the relationship between the duty cycle d1 and d2 is: According to the switch average concept, the switch average current expression of inductor L1 can be obtained: Among them, i pk is the peak value of the inductor L1 current and satisfies: According to the above formula, the average switching current of inductor L1 can be calculated as: According to the power conservation law, we know that the grid-side input power i g v g The rectified input power i 1ave Equal, so combined with the above formula, the expression of switching frequency can be calculated as: The duty cycle d1 is calculated based on the average model of the inductor current switch: Substituting the above formula into the switching frequency expression, the further switching frequency is calculated as: According to the duty cycle d1 and the switching frequency formula, the switch on time can be calculated as:

5. The unified control method for power factor correction of a single-phase DCM Boost converter according to claim 4, characterized in that: Step 5: When the converter operates at light load, the control mode is pulse width modulation control; When the converter operates under heavy load, the control mode is pulse frequency modulation control.

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