Variable frequency control system and circuit board assembly of heat pump compressor and frequency converter

Abstract

The application relates to the technical field of compressors, and discloses a variable-frequency control system of a heat pump compressor, a circuit board assembly and a frequency converter. The variable-frequency control system comprises a phase-shifting transformer, N rectifiers, a DC bus and P inverters. N is an integer greater than or equal to 3, and P is an integer greater than or equal to 1. The input end of the phase-shifting transformer is connected with a power grid, the N output ends of the phase-shifting transformer are one-to-one connected with the input ends of the N rectifiers, and the output ends of the rectifiers are connected with the DC bus. The input end of the inverter is connected with the DC bus, and the output end of the inverter is connected with a load. The phase-shifting transformer is configured to output N groups of three-phase voltages. The rectifiers output a group of pulse DC groups according to the three-phase voltages. The DC bus receives the N groups of pulse DC groups to form DC power. The inverter outputs AC power to the load according to the DC power, thereby reducing the pollution of the frequency converter of the heat pump compressor to the power grid and improving the stability and reliability of the heat pump compressor.

Description

Technical Field

[0001] This application relates to the field of compressor technology, and in particular to a variable frequency control system, circuit board assembly and frequency converter for a heat pump compressor. Background Technology

[0002] Currently, in large-scale heat pump systems (such as district heating and industrial high-temperature heat pumps), the coordinated operation of multiple frequency converters is a key technology for achieving high energy efficiency and high reliability. In order to save costs and simplify the structure, traditional heat pump compressor frequency converters generally adopt 6-pulse or 12-pulse rectification technology and non-common DC frequency converter topology technology.

[0003] However, the frequency converter technology used in this method will cause serious pollution to the power grid, namely the generation of harmonics, which exceeds the GB / T14549 standard. This pollution not only exceeds the total amount, but also contains some specific harmonics that are difficult to eliminate, such as the 5th, 7th, 11th and 13th harmonics, which have high residual levels, exceeding 5%. Utility Model Content

[0004] The purpose of this application is to provide a variable frequency control system, circuit board assembly, and frequency converter for a heat pump compressor, thereby reducing the pollution of the power grid by the frequency converter of the heat pump compressor and improving the stability and reliability of the heat pump compressor.

[0005] To address the aforementioned technical problems, embodiments of this application provide a variable frequency control system for a heat pump compressor, comprising: a phase-shifting transformer, N rectifiers, a DC bus, and P inverters; N is an integer greater than or equal to 3, and P is an integer greater than or equal to 1; the input terminal of the phase-shifting transformer is connected to the power grid, and the N output terminals of the phase-shifting transformer are connected one-to-one to the input terminals of the N rectifiers, with the output terminals of the rectifiers connected to the DC bus; the input terminal of the inverters is connected to the DC bus, and the output terminal of the inverters is connected to the load; the phase-shifting transformer is configured to output N sets of three-phase voltages with phase differences; the rectifiers are configured to output a set of pulsed DC currents according to the corresponding three-phase voltages; the DC bus is configured to receive the N sets of pulsed DC currents to form DC current and output it to the inverters; the inverters are configured to output AC current according to the DC current to supply power to the load.

[0006] Embodiments of this application also provide a circuit board assembly, including: the frequency conversion control system of the above-described heat pump compressor.

[0007] Embodiments of this application also provide a frequency converter, including the circuit board assembly described above.

[0008] In some embodiments, the rectifier is composed of a three-phase bridge rectifier circuit; a group of pulsed DC groups includes 6 pulsed DCs.

[0009] In some embodiments, the phase-shifting transformer is a multi-winding transformer.

[0010] In some embodiments, N is 4; the phase difference between the four three-phase voltages is 15°.

[0011] In some embodiments, the phase-shifting transformer is a three-phase four-winding transformer.

[0012] In some embodiments, the phases of the N groups of three-phase voltages are -22.5°, -7.5°, +7.5°, and +22.5°, respectively.

[0013] In some embodiments, the load is a heat pump compressor.

[0014] In some embodiments, P is 7.

[0015] The embodiments of this application have at least the following advantages: The phase-shifting transformer in this embodiment outputs N sets of three-phase voltages with phase differences. Through the phase shift of the phase-shifting transformer, low-order harmonics cancel each other out on the primary side of the transformer, thereby eliminating low-order harmonics with a large proportion and amplitude, and reducing the pollution of the power grid by the heat pump compressor's inverter. Furthermore, this embodiment uses a common DC bus scheme to ensure balanced power distribution when load power is unequal, avoiding overload of a single inverter (load), thereby improving the stability and reliability of the entire system. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0017] Figure 1 This is a schematic diagram of the structure of a variable frequency control system for a heat pump compressor according to an embodiment of this application; Figure 2 This is another structural schematic diagram of a variable frequency control system for a heat pump compressor according to an embodiment of this application. Detailed Implementation

[0018] As can be seen from the background technology, the inverters of current heat pump compressors cause serious pollution to the power grid.

[0019] Inverters primarily rectify alternating current (AC) into direct current (DC). Currently, inverters in large heat pump systems employ either 6-pulse or 12-pulse rectification technologies. 6-pulse rectification is a common three-phase rectification method, using a rectifier bridge to generate six pulsed DC voltage waveforms within one power cycle. 12-pulse rectification can be viewed as the superposition of two 6-pulse rectifier circuits. A special transformer generates two sets of three-phase voltages with a 30-degree phase difference, which are then rectified separately using two 6-pulse rectifiers and combined for output, producing 12 pulsed DC voltage waveforms within one power cycle. Theoretically, 12-pulse rectification is more advanced than 6-pulse rectification, with fewer harmonics. A non-common DC inverter topology refers to multiple inverters, each with independent rectifier and inverter units, whose DC buses are isolated from each other.

[0020] According to theoretical analysis, 6-pulse rectification will generate characteristic harmonics with a number of 6k±1 (k is a positive integer), namely the 5th, 7th, 11th, 13th, 17th and 19th harmonics. In contrast, 12-pulse rectification will generate characteristic harmonics with a number of 12k±1 (k is a positive integer), namely the 11th, 13th, 23rd and 25th harmonics. Theoretically, 12-pulse rectification can eliminate harmonics below 12k±1, that is, it can eliminate the 5th and 7th harmonics. The lowest characteristic harmonics start from the 11th and 13th.

[0021] These specific harmonics pose certain hazards. For example, the 5th harmonic is a negative sequence component, which can cause the motor to generate reverse torque, leading to overheating and reduced efficiency. The 7th harmonic is a positive sequence component, but it also causes additional heat generation and energy loss. Although the 11th and 13th harmonics have higher frequencies, their large amplitude can still cause problems, and they are more difficult to completely filter out with traditional passive filters.

[0022] However, in the existing 12-pulse rectification, the 5th and 7th harmonics, which should have been eliminated, still exist in large quantities. Moreover, the amplitudes of the 5th and 7th harmonics are relatively large. Theoretically, the lowest order 11th and 13th harmonics also account for a relatively high proportion and have a large amplitude. As a result, the 5th, 7th, 11th and 13th harmonics in the 12-pulse scheme are relatively high, greater than 5%, and the THDi (Total Harmonic Distortion) is greater than 10%, exceeding the GB / T14549 standard, resulting in serious power grid pollution.

[0023] To address the aforementioned technical problems, this application provides a variable frequency control system for a heat pump compressor, comprising: a phase-shifting transformer, N rectifiers, a DC bus, and P inverters; N is an integer greater than or equal to 3, and P is an integer greater than or equal to 1; the input terminal of the phase-shifting transformer is connected to the power grid, and the N output terminals of the phase-shifting transformer are connected one-to-one to the input terminals of the N rectifiers, with the output terminals of the rectifiers connected to the DC bus; the input terminals of the inverters are connected to the DC bus, and the output terminals of the inverters are connected to the load; the phase-shifting transformer is configured to output N sets of three-phase voltages with phase differences; the rectifiers are configured to output a set of pulsed DC currents based on the corresponding three-phase voltages; the DC bus is configured to receive the N sets of pulsed DC currents to form DC current and output it to the inverters; the inverters are configured to output AC current based on the DC current to supply power to the load.

[0024] The phase-shifting transformer in this embodiment outputs N sets of three-phase voltages with phase differences. Through the phase shift of the phase-shifting transformer, low-order harmonics cancel each other out on the primary side of the transformer, thereby eliminating low-order harmonics with a large proportion and amplitude, and reducing the pollution of the power grid by the heat pump compressor's inverter. Furthermore, this embodiment uses a common DC bus scheme to ensure balanced power distribution when load power is unequal, avoiding overload of a single inverter (load), thereby improving the stability and reliability of the entire system.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this application to help readers better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for the convenience of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0026] One embodiment of this application relates to a variable frequency control system for a heat pump compressor, as shown in the schematic diagram below. Figure 1 As shown, the variable frequency control system of the heat pump compressor includes: a phase-shifting transformer 10, N rectifiers 20, a DC bus DC, and P inverters 30; N is an integer greater than or equal to 3, and P is an integer greater than or equal to 1.

[0027] The input terminal of the phase-shifting transformer 10 is connected to the power grid. The N output terminals of the phase-shifting transformer 10 are connected one-to-one to the input terminals of the N rectifiers 20. The output terminals of the rectifiers 20 are connected to the DC bus. The input terminal of the inverter 30 is connected to the DC bus, and the output terminal of the inverter 30 is connected to the load M. The phase-shifting transformer 10 is configured to output N sets of three-phase voltages with phase differences. The rectifiers 20 are configured to output a set of pulsed DC voltages according to the corresponding three-phase voltages. The DC bus is configured to receive the N sets of pulsed DC voltages to form DC power and output it to the inverter 30. The inverter 30 is configured to output AC power according to the DC power to supply power to the load M.

[0028] The phase-shifting transformer 10 of this application outputs N sets of three-phase voltages with phase differences. The phase difference is determined according to the number N. For example, in some embodiments, N is 4, and the phase difference of the four three-phase voltages is 15°. In other embodiments, when N is 3, the phase difference of the three three-phase voltages is 20°. Figure 2 The diagram shown is another structural schematic of the variable frequency control system of the heat pump compressor according to an embodiment of this application.

[0029] In this embodiment, the phase shift of the phase-shifting transformer 10 causes low-order harmonics to cancel each other out on the primary side of the phase-shifting transformer 10, thereby eliminating low-order harmonics with a large proportion and large amplitude. Only high-order harmonics are superimposed and transmitted to the grid side, and the proportion and amplitude of high-order harmonics are small, so they have almost no impact on the grid, thereby reducing the pollution to the grid.

[0030] For example, when N is 4, the phase-shifting transformer 10 cancels out low-order harmonics (such as the 5th, 7th, 11th, and 13th harmonics), and only high-order harmonics, namely the 24k±1st harmonics (such as the 23rd and 25th harmonics), are superimposed and transmitted to the grid side. The lower the order of the harmonics, the more they are generated, the larger their amplitude, and the greater their impact on the grid. Conversely, the higher the order of the harmonics, the less they are generated, the smaller their amplitude, and the smaller their impact on the grid. Therefore, in this embodiment, the phase-shifting transformer 10 only transmits higher-order (such as the 23rd and 25th) harmonics to the grid side. The proportion of high-order harmonics is small, and their amplitude is small, so their impact on the grid is negligible, thereby reducing the pollution of the heat pump compressor's inverter to the grid. The 24-pulse scheme of this embodiment has a THDi of less than 5%, which is significantly better than the 12-pulse scheme with a THDi greater than 10%, thus meeting the requirements of the GB / T14549 standard.

[0031] The phase-shifting transformer 10 in this embodiment is a multi-winding transformer that generates three-phase voltages with different phases through multiple secondary windings. When N is 4, the phase-shifting transformer 10 is a three-phase four-winding transformer, and the phases of the four sets of three-phase voltages output by the phase-shifting transformer 10 are -22.5°, -7.5°, +7.5°, and +22.5°, respectively.

[0032] Each of the N rectifiers 20 is composed of a three-phase bridge rectifier circuit, and each rectifier 20 outputs a set of pulsed DC groups, each set of pulsed DC groups consisting of 6 pulsed DCs. The N sets are superimposed to form N sets of pulsed DC groups. In some embodiments, N is 4, and the 4 sets are superimposed to form 4 sets of pulsed DC groups, i.e., 24 pulsed DCs, with 24 pulses per cycle, thereby achieving high pulse output through phase superposition.

[0033] A three-phase bridge rectifier circuit consists of six switching devices (e.g., S1, S2, S3, S4, S5, S6) and their anti-parallel diodes (e.g., D1, D2, D3, D4, D5, D6). When none of the six switching devices are driven, and only their anti-parallel diodes are used, the circuit forms a three-phase uncontrolled diode rectifier bridge, i.e., a 6-pulse rectifier bridge. The 6-pulse rectifier bridge outputs 6 pulses of DC, and the pulsation frequency of the 6 pulses is 6 times the grid frequency, i.e., 6 × 50 Hz = 300 Hz.

[0034] Afterwards, N groups of pulsed DC are transmitted to the DC bus. For example, after four 6-pulse DCs with a phase difference of 15° are superimposed, a DC with a pulsation frequency of 4×6×50Hz is formed on the DC bus. The ripple of this DC is very small and very close to that of an ideal smooth DC.

[0035] Because the grid-side harmonic suppression capability is easily lost, DC-side voltage fluctuations are aggravated, and circulating current problems are easily caused when the load power of the inverter branch is unequal in the related technology, the DC bus DC of this application embodiment transmits the DC power to the inverter 30. The common DC bus DC scheme ensures that the power can be balanced when the load M power is unequal, avoids overload of a single inverter 30 and load M, thereby improving the stability and reliability of the entire system.

[0036] Inverter 30 receives DC power transmitted from the DC bus and outputs AC power to supply power to the load M. In this embodiment, after receiving DC power generated by a 24-pulse DC converter, inverter 30 further smooths it using its own DC bus capacitor, and then independently generates the required three-phase AC power entirely by relying on its own high-frequency PWM modulation technology. The ripple of the front-stage 24-pulse rectification is very small, very close to ideal smooth DC, providing a near-ideal power environment for the stable and efficient operation of the subsequent inverter 30.

[0037] In this embodiment, the load M is a heat pump compressor. There is a one-to-one correspondence between the inverter 30 and the load M. The number of inverters 30 can be set according to actual needs. In some embodiments, the number P of inverters 30 is 7, while in other embodiments, the number P of inverters 30 can be 3, 4, 5, 6, etc. This embodiment ensures balanced power distribution when the load M has unequal power by using a common DC bus for the inverters 30, avoiding overload of a single inverter 30 (load M), thereby improving the stability and reliability of the entire system.

[0038] In practical applications, the variable frequency control system in this application embodiment can be used as a frequency converter for the heat pump compressor, which is the "speed regulator" of the heat pump compressor. The frequency converter first converts the AC power from the power grid into DC power, and then inverts the DC power into AC power with a variable frequency, thereby controlling the compressor speed and realizing on-demand output.

[0039] After summing N groups of 6-pulse DC, a 6N-pulse DC is obtained. When N is 4, the DC current summed on the DC bus is a 24-pulse DC. The ripple of the 24-pulse DC is very small, close to ideal smooth DC, resulting in smaller ripple at the input terminal (i.e., DC side) of inverter 30 and smoother voltage. For example, the ripple factor of 12-pulse DC is about 4%, while the ripple factor of 24-pulse DC in this embodiment is less than 1%. The ripple factor on the DC side of inverter 30 is significantly reduced, resulting in smoother voltage on the DC side of inverter 30. At the same time, the temperature rise of the power devices in inverter 30 is significantly reduced, and the capacitor life is extended, making the operation of the load M, such as the heat pump compressor, more stable. Furthermore, the embodiment of this application is an improvement on the frequency converter, which can directly replace the traditional frequency converter without modifying the power grid infrastructure.

[0040] Another aspect of this application provides a circuit board assembly, including: a frequency conversion control system for a heat pump compressor as described in any of the above embodiments.

[0041] It is not difficult to see that this embodiment is a circuit board assembly embodiment corresponding to the circuit embodiment, and this embodiment can be implemented in conjunction with the circuit embodiment. The relevant technical details mentioned in the circuit embodiment are still valid in this embodiment, and will not be repeated here to reduce repetition. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to the circuit embodiment.

[0042] Furthermore, in order to highlight the innovative aspects of this application, no units that are not closely related to solving the technical problems proposed in this application are introduced in this embodiment, but this does not mean that there are no other units in this embodiment.

[0043] Another aspect of this application provides a frequency converter, including: a circuit board assembly as described in the above embodiment.

[0044] The above division of various components is only for clarity of description. In implementation, they can be combined into one component or some components can be split into multiple components. As long as they include the same logical relationship, they are all within the scope of protection of this patent.

[0045] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing this application, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of this application.

Claims

1. A variable frequency control system for a heat pump compressor, characterized in that, include: Phase-shifting transformer, N rectifiers, DC bus, P inverters; N is an integer greater than or equal to 3, and P is an integer greater than or equal to 1; The input terminal of the phase-shifting transformer is connected to the power grid, and the N output terminals of the phase-shifting transformer are connected one-to-one to the input terminals of the N rectifiers. The output terminals of the rectifiers are connected to the DC bus. The input terminal of the inverter is connected to the DC bus, and the output terminal of the inverter is connected to the load. The phase-shifting transformer is configured to output N sets of three-phase voltages with phase differences; the rectifier is configured to output a set of pulsed DC currents according to the corresponding three-phase voltages; the DC bus is configured to receive the N sets of pulsed DC currents to form DC current and output it to the inverter; the inverter is configured to output AC current according to the DC current to supply power to the load.

2. The frequency conversion control system according to claim 1, characterized in that, The rectifier is composed of a three-phase bridge rectifier circuit; one group of the pulsed DC groups includes 6 pulsed DCs.

3. The frequency conversion control system according to claim 1, characterized in that, The phase-shifting transformer is a multi-winding transformer.

4. The frequency conversion control system according to claim 1, characterized in that, N is 4; the phase difference between the four three-phase voltages is 15°.

5. The frequency conversion control system according to claim 4, characterized in that, The phase-shifting transformer is a three-phase four-winding transformer.

6. The frequency conversion control system according to claim 4, characterized in that, The phases of the three-phase voltages in group N are -22.5°, -7.5°, +7.5°, and +22.5°, respectively.

7. The frequency conversion control system according to claim 1, characterized in that, The load is a heat pump compressor.

8. The frequency conversion control system according to claim 7, characterized in that, The value of P is 7.

9. A circuit board assembly, characterized in that, include: The variable frequency control system for the heat pump compressor according to any one of claims 1 to 8.

10. A frequency converter, characterized in that, include: The circuit board assembly of claim 9.

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