Active power factor correction frequency converter for driving heat pump BLDC compressor

Abstract

The invention provides an active power factor correction frequency converter for driving a heat pump BLDC compressor, and belongs to the field of frequency converters. The circuit comprises an active power factor correction circuit, a frequency conversion circuit and a control circuit. The control circuit controls the switching frequency of the frequency conversion circuit, specifically, the rotating speed requirement of a heat pump BLDC compressor is set to be n, the highest driving switching frequency of the compressor is set to be f01, and the highest rotating speed is set to be n0; when # imgabs0 #, the control circuit adjusts the switching frequency of the frequency conversion circuit to # imgabs1 #, and when # imgabs2 #, the control circuit adjusts the switching frequency of the frequency conversion circuit to the switching frequency corresponding to the linear proportion between # imgabs3 # and # imgabs4 #; and when # imgabs 5 #, the control circuit adjusts the switching frequency of the frequency conversion circuit to the set f01. The switching frequency of the frequency conversion circuit is controlled through the control circuit, the compressor can be normally driven under the low, medium and high rotating speed requirements, the loss of a power switch is reduced during low-power output, the waveform of driving current is closer to sine waves during high-power output, and the compressor can work more efficiently.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency converters, and in particular to an active power factor correction frequency converter for driving a heat pump BLDC compressor. Background Art

[0002] When a typical heat pump inverter receives three-phase AC input, it is rectified into DC power through a rectifier circuit after AC filtering, and then controlled by a control circuit to output the variable frequency circuit to drive the heat pump BLDC compressor. However, the following deficiencies still exist in typical heat pump inverters: the three-phase AC power is directly rectified into DC power by the rectifier circuit, and the AC current cannot follow the changes in the AC voltage, so it has a relatively large impact on the harmonics of the AC input grid current, which may endanger the safety of the grid in severe cases; as the output power increases, the rectified DC bus voltage decreases, resulting in the variable frequency output voltage being lower than the maximum required working voltage of the compressor, making it difficult for the compressor to reach the maximum speed, and the heating efficiency of the heat pump is difficult to guarantee; the variable frequency circuit controlled by the control circuit generally only changes the speed of the driving compressor according to the needs of the heat pump system, and the switching frequency of the power switch of the variable frequency circuit is fixed, so the switching loss accounts for a relatively large proportion in the case of low output power, resulting in a large loss of the inverter.

[0003] The publication number is CN113726138A, which discloses a frequency conversion circuit, frequency converter, compressor and air conditioning equipment for achieving harmonic suppression. It uses a rectifier module to turn on or off the rectifier element inside it, thereby controlling the conduction state between the phases of the AC power supply, changing its own charge and discharge state according to the conduction state between the phases of the AC power supply, and then triggering the rectifier element inside the rectifier module to turn on or off. It can make the input current of the frequency conversion circuit closer to a sine wave, suppress the harmonic content of the input current to a certain extent, achieve power factor correction, and effectively raise the DC bus voltage to avoid the impact of the bus voltage being too low on the compressor. However, it still does not solve the problem that the power switch of the frequency conversion circuit has a large loss ratio under low power conditions, affecting the operation of the compressor. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to solve the problem that the existing three-phase AC powered heat pump uses three-phase direct rectification to DC power and then drives the heat pump compressor through frequency conversion, resulting in large grid current harmonics, a decrease in the rectified DC bus voltage when the output increases, and a large proportion of losses in the power switch of the frequency conversion circuit under low power conditions.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: an active power factor correction inverter for driving a heat pump BLDC compressor, comprising an active power factor correction circuit, a frequency conversion circuit and a control circuit; the control circuit controls the switching frequency of the frequency conversion circuit, specifically:

[0006] Set the speed requirement of the heat pump BLDC compressor to n, and the maximum drive switching frequency of the heat pump BLDC compressor to f 01 , the maximum speed is n0;

[0007] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to

[0008] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to The linear ratio between corresponds to the switching frequency;

[0009] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to the set maximum drive switching frequency f of the heat pump BLDC compressor, 01 .

[0010] The present invention controls the frequency of the frequency conversion circuit through a control circuit according to the speed requirement, which not only ensures that the compressor is normally driven under low, medium and high speed requirements, but also reduces the loss of the power switch at low power output, and makes the driving current waveform closer to a sine wave at high power output, so that the compressor can be in a more efficient working state.

[0011] Preferably, the control circuit controls the output voltage of the active power factor correction circuit, specifically:

[0012] Set the rated output voltage of the active power factor correction circuit to U0;

[0013] when When , the control circuit adjusts the output voltage of the active power factor correction circuit to 0.95U0;

[0014] when When , the control circuit adjusts the output voltage of the active power factor correction circuit to 0.975U0;

[0015] when When , the control circuit adjusts the output voltage of the active power factor correction circuit to the rated output voltage U0.

[0016] The present invention utilizes a control circuit to adjust the output voltage of an active power factor correction circuit, thereby ensuring the normal operation of the compressor, especially in the case of high power output, ensuring that the rectified DC bus voltage can support high-speed operation of the compressor after frequency conversion output, thereby ensuring the heating effect of the heat pump.

[0017] Preferably, the control circuit also controls the switching frequency of the active power factor correction circuit, specifically:

[0018] Set the switching frequency of the active power factor correction circuit to f0;

[0019] when When the control circuit adjusts the switching frequency of the active power factor correction circuit to

[0020] when When the control circuit adjusts the switching frequency of the active power factor correction circuit to

[0021] when When , the control circuit adjusts the switching frequency of the active power factor correction circuit to the set active power factor correction circuit switching frequency f0.

[0022] The present invention utilizes a control circuit to control the switching frequency of an active power factor correction circuit, so that when the compressor is at a low speed and low power output, the switching loss and inductance loss of the active power factor correction circuit are reduced.

[0023] Preferably, it also includes an AC input interface, an AC filter module and a frequency conversion output interface, and the AC input interface, the AC filter module, the active power factor correction circuit, the frequency conversion circuit and the frequency conversion output interface are connected in sequence.

[0024] Preferably, the AC filter module performs EMI processing on the three-phase AC input, that is, eliminates electromagnetic interference.

[0025] Preferably, the active power factor correction circuit comprises a three-phase diode rectifier bridge and three bidirectional switches, and each phase of the three-phase diode rectifier bridge is connected to a bidirectional switch.

[0026] Preferably, the bidirectional switch is composed of two switch tubes connected back to back.

[0027] Preferably, the specific process of power factor correction performed by the active power factor correction circuit is: the active power factor correction circuit monitors the frequency, phase and amplitude of the input in real time, and controls the opening or closing of the bidirectional switch to make the waveform of the input current and the input voltage waveform have the same change trend in frequency, phase and amplitude.

[0028] Preferably, the active power factor correction circuit converts the AC input voltage into a DC voltage using a three-phase diode rectifier bridge while performing power factor correction.

[0029] Preferably, the diodes in the three-phase diode rectifier bridge are fast recovery diodes or SiC diodes.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] (1) According to the speed requirement of the heat pump BLDC compressor, the switching frequency of the frequency conversion circuit is controlled by the control circuit. Within the working switching frequency range of the BLDC compressor, when the corresponding required speed changes from low to high, the switching frequency also changes from small to large, so that when the BLDC compressor works at a low speed, the switching loss of the frequency conversion circuit is reduced. When the BLDC compressor works at a high speed, the high switching frequency makes the driving current waveform closer to a sine wave, and the BLDC compressor works in a more efficient state;

[0032] (2) The active power factor correction circuit is used to make the input current waveform and the input voltage waveform have the same frequency, phase and amplitude change trend, so as to achieve a power factor close to 1, reduce energy waste, and improve circuit efficiency; at the same time, it generates as small current harmonics as possible, eliminating the large current harmonic hazards of common inverters; it can also boost the AC voltage to a stable DC voltage, and after the frequency conversion output, it can stably drive the compressor;

[0033] (3) According to the speed requirement of the heat pump BLDC compressor, the control circuit is used to control the output voltage and switching frequency of the active power factor correction circuit. When the required speed of the BLDC compressor increases from low to high, the switching frequency and output voltage also increase from small to large. This reduces the switching loss and inductance loss of the active power factor correction circuit when the inverter is outputting at low power. When the inverter is outputting at high power, it ensures that the DC bus voltage can drive the compressor to operate at high speed after being output by the frequency conversion circuit, and the conversion efficiency of the BLDC compressor is maximized. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural block diagram of the active power factor correction inverter of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not 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.

[0036] Example

[0037] like Figure 1As shown, this embodiment provides an active power factor correction inverter for driving a heat pump BLDC compressor, which includes an AC input interface, an AC filter module, an active power factor correction circuit, a frequency conversion circuit and a frequency conversion output interface, which are connected in sequence, and also includes a control circuit. This control circuit is used to control the switching frequency and output voltage of the active power factor correction circuit, and is also used to control the switching frequency of the frequency conversion circuit.

[0038] The working principle of the active power factor correction inverter of this embodiment is introduced as follows:

[0039] The three-phase AC input enters the inverter through the AC input interface, and then passes through the AC filter module for EMI processing, that is, electromagnetic interference elimination. The AC input processed by the AC filter module enters the active power factor correction circuit for power factor correction and boosting;

[0040] The active power factor correction circuit in this embodiment belongs to the three-phase Vienna topology, including a three-phase diode rectifier bridge and three bidirectional switches. Each phase of the three-phase diode rectifier bridge is connected to a bidirectional switch, and the bidirectional switch is composed of two switch tubes connected back to back. Its advantages are that the main circuit has fewer power devices, only three drive circuits are needed, and the six switch tubes only need to withstand half of the DC side voltage. The power devices on the current conduction path are the least, and the conduction loss is low. In another embodiment, other active power factor correction circuits with high-frequency switches are applicable;

[0041] The AC input enters the active power factor correction circuit, which converts the AC input into DC using a three-phase diode rectifier bridge. The active power factor correction circuit monitors the input frequency, phase and amplitude in real time, and controls the on or off of the bidirectional switch or adjusts the duty cycle of the switch to make the input current follow the input voltage waveform, which has the same changing trend as the frequency, phase and amplitude of the voltage waveform, thereby achieving a power factor close to 1, reducing the waste of reactive power and energy, and improving the efficiency of the circuit; at the same time, it generates current harmonics as small as possible to eliminate the harm of current harmonics to the power grid.

[0042] At this time, the control circuit adjusts the switching frequency and output voltage of the active power factor correction circuit according to the BLDC compressor speed requirement n set by the heat pump system instruction. At this time, the output voltage is a stable DC voltage, specifically:

[0043] Set the switching frequency of the active power factor correction circuit to f0 and the rated output voltage to U0;

[0044] when When the control circuit adjusts the switching frequency of the active power factor correction circuit to At the same time, the output voltage is adjusted to 0.95U0, thereby reducing the loss of the power switch and the inductance loss, and ensuring that the compressor can be driven normally when the inverter outputs low power;

[0045] when When the control circuit adjusts the switching frequency of the active power factor correction circuit to At the same time, the output voltage is adjusted to 0.975U0, thereby reducing the switching loss and inductance loss of the power switch, and ensuring that the compressor can be driven normally when the inverter has medium power output;

[0046] when When the control circuit adjusts the switching frequency of the active power factor correction circuit to the set active power factor correction circuit switching frequency f0, the output voltage is adjusted to the rated output voltage U0, thereby ensuring that in the high power output stage of the inverter, the DC bus voltage can drive the compressor to run at a high speed after being output by the frequency conversion circuit. At this time, the compressor is in an efficient working state.

[0047] The input undergoes power factor correction and voltage boost in the active power factor correction circuit, and after adjusting its switching frequency and output voltage within a certain range, it outputs a stable DC voltage and then enters the frequency conversion circuit;

[0048] The control circuit also adjusts the switching frequency of the frequency conversion circuit according to the BLDC compressor speed requirement n set by the heat pump system instruction, specifically:

[0049] Set the speed requirement of the heat pump BLDC compressor to n and the maximum drive switching frequency to f 01 , the maximum speed is n0;

[0050] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to This reduces the switching loss of the power switch and ensures that the BLDC compressor can be driven at a low speed.

[0051] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to The linear ratio between φ and φ corresponds to the switching frequency, thereby reducing the switching loss of the power switch while ensuring that the BLDC compressor can be driven to operate at a medium speed;

[0052] when When the control circuit adjusts the switching frequency of the frequency conversion circuit to the set maximum drive switching frequency f of the heat pump BLDC compressor, 01 , ensuring that the BLDC compressor is driven normally at high speed. At the same time, the higher frequency makes the driving current waveform closer to a sine wave, and the compressor works in a more efficient state.

[0053] At this time, the input is output to the frequency conversion output interface after passing through the frequency conversion circuit, connecting and driving the BLDC compressor, and the heat pump starts working.

[0054] This embodiment uses a control circuit to adjust the switching frequency and output voltage of the active power factor correction circuit and the switching frequency of the frequency conversion circuit according to the speed requirement of the BLDC compressor. It can drive the compressor to work normally at the required speed in different power output stages of the inverter. In particular, it can reduce the switching loss of the power switch when the power output is low and the compressor is running at a low speed. When the power output is high and the compressor is running at a high speed, it can continuously drive the compressor to run at a high speed, so that the compressor is in a state of high efficiency.

[0055] That is, this embodiment can not only ensure the normal operation of the heat pump BLDC compressor through the change of switching frequency and the adjustment of DC voltage, but also minimize the overall loss of the inverter at medium and low power output, ensure high-speed operation of the compressor at high power output, and improve the energy efficiency of the heat pump.

[0056] The parameter used to measure the energy efficiency of the heat pump is the performance parameter cop, and its formula is: Where P 制热量 is the thermal power of the heat pump, P in电功率 It is the AC input electric power of the heat pump, which is mainly the AC input power of the inverter.

[0057] Since the input power is the sum of the output power and the loss, when the switching loss and inductance loss of the active power factor correction circuit in the inverter are reduced and the switching loss of the frequency conversion circuit is reduced, the AC input power P in电功率 Decreases, which increases cop, that is, the energy efficiency of the heat pump is improved.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An active power factor correction inverter for driving a heat pump BLDC compressor, characterized in that: It includes an active power factor correction circuit, a frequency conversion circuit and a control circuit; the control circuit controls the switching frequency of the frequency conversion circuit, specifically: Set the speed requirement of the heat pump BLDC compressor to n and the maximum drive switching frequency to f 01 , the maximum speed is n0; when When the control circuit adjusts the switching frequency of the frequency conversion circuit to when When the control circuit adjusts the switching frequency of the frequency conversion circuit to to The linear ratio between corresponds to the switching frequency; when When the control circuit adjusts the switching frequency of the frequency conversion circuit to the set maximum driving switching frequency f of the heat pump BLDC compressor, 01 .

2. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 1, characterized in that: The control circuit controls the output voltage of the active power factor correction circuit, specifically: Set the rated output voltage of the active power factor correction circuit to U0; when When , the control circuit adjusts the output voltage of the active power factor correction circuit to 0.95U0; when When , the control circuit adjusts the output voltage of the active power factor correction circuit to 0.975U0; when When , the control circuit adjusts the output voltage of the active power factor correction circuit to the rated output voltage U0.

3. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 2, characterized in that: The control circuit also controls the switching frequency of the active power factor correction circuit, specifically: Set the switching frequency of the active power factor correction circuit to f0; when When the control circuit adjusts the switching frequency of the active power factor correction circuit to when When the control circuit adjusts the switching frequency of the active power factor correction circuit to when When , the control circuit adjusts the switching frequency of the active power factor correction circuit to the set active power factor correction circuit switching frequency f0.

4. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 1, characterized in that: It also includes an AC input interface, an AC filter module and a frequency conversion output interface, wherein the AC input interface, the AC filter module, the active power factor correction circuit, the frequency conversion circuit and the frequency conversion output interface are connected in sequence.

5. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 4, characterized in that: The AC filter module performs EMI processing on the three-phase AC input, that is, eliminates electromagnetic interference.

6. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 4, characterized in that: The active power factor correction circuit comprises a three-phase diode rectifier bridge and three bidirectional switches, and each phase of the three-phase diode rectifier bridge is connected to a bidirectional switch.

7. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 6, characterized in that: The bidirectional switch is composed of two switch tubes connected back to back.

8. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 7, characterized in that: The specific process of the active power factor correction circuit for power factor correction is as follows: the active power factor correction circuit monitors the frequency, phase and amplitude of the input in real time, and controls the on or off of the bidirectional switch to make the waveform of the input current and the input voltage waveform have the same change trend in frequency, phase and amplitude.

9. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 8, characterized in that: The active power factor correction circuit converts the AC input voltage into a DC voltage using a three-phase diode rectifier bridge while performing power factor correction.

10. An active power factor correction inverter for driving a heat pump BLDC compressor according to claim 9, characterized in that: The diodes in the three-phase diode rectifier bridge are fast recovery diodes or SiC diodes.

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