DC bus small-capacity capacitor frequency conversion control circuit and frequency conversion equipment

Abstract

The invention discloses a DC bus small-capacity capacitor frequency conversion control circuit and frequency conversion equipment, including a rectifier, a DC bus, a small-capacity capacitor, an inverter, an inverter control module, a power supply switch, an inverter control module power supply circuit and a power supply control module; the power supply switch is connected between the rectifier and the AC input; the inverter control module power supply circuit is connected to the AC input to provide power for the inverter control module; the power supply control module controls the power supply switch to close after the inverter control module power supply circuit runs stably, so that the AC input is connected to the rectifier. After the whole machine is powered on and the AC input is provided, the inverter control module power supply circuit is first started to provide working power for the inverter control module. After the AC input is stable, the power supply control module controls the power supply switch to close so that the AC input is connected to the rectifier, and the inverter control circuit and the inverter working circuit are powered on in a time-sharing manner in a two-level power-on control mode, thereby improving the reliability of the frequency conversion control.

Description

Technical Field

[0001] The invention belongs to the technical field of motor control, and in particular relates to a direct current bus small-capacity capacitor frequency conversion control circuit and frequency conversion equipment. Background Art

[0002] There are two types of products in the air-conditioning market: fixed-speed air conditioners and variable-frequency air conditioners. Fixed-speed air conditioners generate huge impact current when starting, affecting the operation of other electrical appliances in the power grid. A large amount of harmonics will be generated during operation, increasing the load on the power grid and affecting the safety of the power grid. However, because fixed-speed air conditioners have low costs, they occupy a large proportion of the air-conditioning market.

[0003] The DC filter link of the variable frequency control of the traditional variable frequency air conditioner is composed of electrolytic capacitors of thousands or even thousands of microfarads. However, the capacity of the electrolytic capacitor is large, and the current distortion on the power input side causes high harmonic components, and the power factor is low. In order to improve the harmonics caused by the charging and discharging of the filter capacitor, it is necessary to add a PFC (Power Factor Correction) circuit to correct the power factor and solve the harmonic problem. The switching devices in the PFC circuit will produce a large power loss and a large EMI (Electro Magnetic Interference) interference at a higher switching frequency. If this problem is not solved, it is necessary to increase the EMI filtering cost. Therefore, the cost of the traditional variable frequency control circuit is high, and the electrolytic capacitor and the power device of the PFC circuit are the failure-prone devices of the variable frequency controller, among which the life of the electrolytic capacitor is more obviously affected by temperature and voltage.

[0004] In view of the above problems, the prior art has proposed a solution to replace the electrolytic capacitor with a small-capacitance film capacitor, which can omit the PFC part and the EMI filtering part, realize the miniaturization and low cost of the frequency conversion control circuit, and eliminate the problem of short life of the electrolytic capacitor. However, the capacity of the small-capacitance film capacitor is usually small, resulting in unstable DC bus voltage. When the system impedance matching is not appropriate, it causes system resonance and system overvoltage fault. To overcome these problems, the existing solution is to detect parameters such as AC input voltage and bus voltage, and use a drive algorithm to solve the DC bus voltage stability problem. Summary of the invention

[0005] The present application provides a DC bus small-capacity capacitor frequency conversion control circuit and frequency conversion equipment, constructs a frequency conversion control circuit using small-capacitance film capacitors to achieve the stability design of the DC bus voltage, and can provide various parameters of the driving algorithm for solving harmonic problems and DC bus voltage stability.

[0006] In order to achieve the above technical effects, this application adopts the following technical solutions:

[0007] A DC bus small-capacity capacitor frequency conversion control circuit is proposed, comprising a rectifier, a DC bus, a small-capacity capacitor, an inverter and an inverter control module; the two output ends of the rectifier are connected to the DC bus, and the small-capacity capacitor and the inverter are connected in parallel with the DC bus in sequence; the circuit also comprises a power supply switch, an inverter control module power supply circuit and a power supply control module; the power supply switch is connected between the rectifier and the AC input; the inverter control module power supply circuit is connected to the AC input to provide power for the inverter control module; the power supply control module is used to control the power supply switch to be closed after the inverter control module power supply circuit operates stably, so that the AC input is connected to the rectifier.

[0008] A frequency conversion device is proposed, including a DC bus small-capacity capacitor frequency conversion control circuit, the DC bus small-capacity capacitor frequency conversion control circuit includes a rectifier, a DC bus, a small-capacity capacitor, an inverter and an inverter control module; the two output ends of the rectifier are connected to the DC bus, and the small-capacity capacitor and the inverter are connected in parallel with the DC bus in sequence; it also includes a power supply switch, an inverter control module power supply circuit and a power supply control module; the power supply switch is connected between the rectifier and the AC input; the inverter control module power supply circuit is connected to the AC input to provide power for the inverter control module; the power supply control module is used to control the power supply switch to be closed after the inverter control module power supply circuit operates stably, so that the AC input is connected to the rectifier.

[0009] Compared with the prior art, the advantages and positive effects of the present application are as follows: the DC bus small-capacity capacitor frequency conversion control circuit proposed in the present application includes a rectifier, a DC bus, a small-capacity capacitor, an inverter, an inverter control module, a power supply switch, an inverter control module power supply circuit and a power supply control module; the inverter control module power supply circuit is directly connected to the AC input, and a power supply switch is connected between the AC input and the rectifier. When the power supply switch is disconnected, the AC input is separated from the rectifier. After the whole machine is powered on and the AC input is provided, the inverter control module power supply circuit is first started to provide working power for the inverter control module. After it is stable, the power supply control module controls the power supply switch to close so that the AC input is connected to the rectifier, and then the rectifier outputs DC power to the inverter to realize the power-on of the inverter bus power supply. Through this two-level power-on control method, the inverter control circuit and the inverter working circuit are powered on in time, thereby improving the reliability of the frequency conversion control. A surge voltage absorption circuit is added. When a momentary surge overvoltage occurs in the bus voltage of the second-stage circuit, the surge energy can be discharged to the bus capacitor of the first-stage circuit through the surge voltage absorption circuit, thereby avoiding overvoltage damage to the second-stage power device, improving reliability, and achieving stability design of the DC bus voltage.

[0010] After reading the detailed description of the embodiments of the present application in conjunction with the accompanying drawings, other features and advantages of the present application will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a circuit embodiment diagram of a DC bus small-capacity capacitor frequency conversion control circuit proposed in this application;

[0012] Figure 2 This is a diagram of an embodiment of the DC bus overvoltage protection circuit proposed in this application;

[0013] Figure 3 This is a diagram of an embodiment of the AC input voltage detection circuit proposed in this application. DETAILED DESCRIPTION

[0014] The specific implementation of the present application is further described in detail below with reference to the accompanying drawings.

[0015] like Figure 1 As shown, the DC bus small-capacity capacitor frequency conversion control circuit proposed in the present application includes a rectifier U1, a DC bus, a small-capacity capacitor C1, an inverter U, an inverter control module U2, a power supply switch K1, an inverter control module power supply circuit U3 and a power supply control module U4; the two output terminals b1 and b2 of the rectifier U1 are connected to the DC bus, and the small-capacity capacitor C1 and the inverter U are connected to the DC bus in parallel in sequence; the power supply switch K1 is connected between the rectifier U1 and the AC input AC; the inverter control module power supply circuit U3 is connected to the AC input AC to provide working power for the inverter control module U2; the power supply control module U4 is used to control the power supply switch K1 to close after the inverter control module power supply circuit U3 runs stably, so that the AC input AC is connected to the rectifier U1; the inverter U is connected to the motor COMP.

[0016] The inverter control module power supply circuit U3 is directly connected to the AC input AC. A power supply switch K1 is connected between the AC input AC and the rectifier U1. When the power supply switch K1 is disconnected, the AC input AC is separated from the rectifier U1. After the whole machine is powered on and the AC input AC is provided, the inverter control module power supply circuit U3 will be started first to provide working power for the inverter control module U2. After it is stable, the power supply control module U4 controls the power supply switch K1 to close so that the AC input AC is connected to the rectifier U1, and then the rectifier U1 outputs DC power to the inverter U, so that the inverter bus power supply is powered on. Through this two-level power-on control method, the inverter control circuit and the inverter working circuit are powered on in time, which improves the reliability of the frequency conversion control and realizes the stability design of the DC bus voltage.

[0017] Specifically, Figure 1As shown, the inverter control module power supply circuit U3 proposed in the present application includes a first resistor R1, a first diode D1, an electrolytic capacitor E1, a switch tube IC1 and a transformer T; one end of the first resistor R1 is connected to the AC input AC, the other end of the first resistor R1 is connected to the positive electrode of the first diode D1, the negative electrode of the first diode D1 is connected to one end of the primary coil of the transformer T, the other end of the primary coil of the transformer T is connected to the second input end b of the switch tube IC1, and the output end c of the switch tube IC1 is grounded; the first input end a of the switch tube IC1 is connected to the positive end of the electrolytic capacitor E1 through a resistor; the positive end of the electrolytic capacitor E1 is connected to the negative electrode of the first diode D1, and the negative end of the electrolytic capacitor E1 is grounded.

[0018] After the whole machine is powered on, the AC input AC is half-wave rectified by the first diode D1 after passing through the first resistor R1 to output pulsating DC. The pulsating DC output charges the electrolytic capacitor E1. When the voltage of the electrolytic capacitor E1 reaches the set value, the switch tube IC1 performs switching control to supply power to the inverter control module U2 and / or the power supply control module U4.

[0019] After the inverter control module power supply circuit U3 works stably, that is, after outputting a stable working power supply, the power supply control module U4 controls the power supply switch K1 to close. The output stability of the inverter control module power supply circuit U3 can be measured by time setting or sampling data. For example, the power supply control module U4 can control the power supply switch K1 to close after a time period that satisfies the inverter control module power supply circuit U3's stable operation, or, by sampling the output voltage signal of the inverter control module power supply circuit to determine whether the preset voltage is met, and close the power supply switch K1 after the preset voltage is met.

[0020] The DC bus small-capacity capacitor frequency conversion control circuit proposed in this application also includes a DC bus surge voltage absorption circuit U5; Figure 1 As shown, the DC bus surge voltage absorption circuit U5 includes a second diode D2, a second resistor R2 and an electrolytic capacitor E1; the positive electrode of the second diode D2 is connected to the first DC output terminal b1 of the rectifier U1, the negative electrode of the second diode D21 is connected to the second resistor R2, and the other end of the second resistor R2 is connected to the negative electrode of the first diode D1 and the positive electrode of the electrolytic capacitor E1. Since the small capacitance capacitor on the DC bus is only a thin film capacitor of tens of microfarads, when the instantaneous surge voltage is fed back on the inverter side, the bus voltage Vdc1 will increase instantaneously, which may cause damage to the inverter end. Therefore, in the DC bus surge voltage absorption circuit U5 in this application, when Vdc1>Vdc2, the DC bus voltage charges the electrolytic capacitor E1 through the second diode D2 and the second resistor R2, reduces the voltage value of Vdc1, and maintains the stability of the DC bus voltage.

[0021] The DC bus small-capacity capacitor frequency conversion control circuit in this application also includes a DC bus overvoltage protection circuit; Figure 2 As shown, it includes a reference voltage circuit and a first comparator U7; the reference voltage circuit is, for example, the resistor divider circuit in the figure, the output of the reference voltage circuit is connected to the first input terminal (the positive phase terminal in the figure) of the first comparator U7, and the second input terminal (the negative phase terminal in the figure) of the first comparator U7 is connected to the DC bus, or the positive terminal of the electrolytic capacitor, or the output terminal of the resistor divider circuit connected in parallel with the electrolytic capacitor E1 as shown in the figure, and any test point that can reflect the DC bus voltage; the output terminal of the first comparator U7 is connected to the inverter control module U2; when the DC bus voltage is higher than the output voltage of the reference voltage circuit, the inverter control module U2 stops the inverter output according to the output control of the first comparator, so as to realize rapid protection of the inverter.

[0022] The DC bus small-capacity capacitor frequency conversion control circuit proposed in this application also provides various parameters for providing a driving algorithm to solve the harmonic problem and DC bus voltage stability, specifically, for example Figure 2 The bus voltage detection circuit U8 shown in the figure; the bus voltage detection circuit is connected to the DC bus and is used to obtain and output the voltage on the DC bus; the specific bus voltage detection circuit is, for example, the output of the resistor divider circuit shown in the figure or other circuits that can realize sampling of the bus voltage, which is not limited in this application, and the output Vdc1-AD / Vdc2-AD of the bus voltage detection circuit is output to the MCU or drive module for software protection control.

[0023] like Figure 3 As shown, the DC bus small-capacity capacitor frequency conversion control circuit proposed in the present application also includes an AC input voltage detection circuit; including a resistor network circuit U10, a bias voltage setting circuit U11 and a second comparator U12; the input end of the resistor network circuit U10 is connected to the AC input AC, and the first output end of the resistor network circuit is connected to the first input end of the second comparator (the positive end shown in the figure); the second output end of the resistor network is connected to the second input end of the second comparator (the inverting end shown in the figure); the output of the bias voltage setting circuit U11 is connected to the first input end of the second comparator, and an AC bidirectional detection method is adopted to apply a bias voltage to the detection signal so that the output signal is a voltage signal of 0-5V. Through this circuit, control modules such as MCU and drive module can detect the change of input voltage in real time to perform drive control, wherein Vac-AD is the analog detection output signal of the AC input voltage.

[0024] Based on the above-mentioned DC bus small-capacity capacitor frequency conversion control circuit, the present application also protects a frequency conversion device such as a variable-frequency air conditioner, which is applied with the above-mentioned DC bus small-capacity capacitor frequency conversion control circuit, the inverter control module power supply circuit is directly connected to the AC input, and a power supply switch is connected between the AC input and the rectifier. The power supply switch is disconnected to separate the AC input from the rectifier. After the whole machine is powered on and the AC input is provided, the inverter control module power supply circuit is first started to provide working power for the inverter control module. After it is stable, the power supply control module controls the power supply switch to close so that the AC input is connected to the rectifier, and then the rectifier outputs DC power to the inverter, so as to realize the power-on of the inverter bus power supply. Through this two-level power-on control method, the inverter control circuit and the inverter working circuit are powered on in time, thereby improving the reliability of the frequency conversion control. By adding a surge voltage absorption circuit, when the bus voltage of the second-level circuit experiences an instantaneous surge overvoltage, the surge energy can be discharged to the bus capacitor of the first-level circuit through the surge voltage absorption circuit, avoiding overvoltage damage to the second-level power device, improving reliability, and achieving a stable design for the DC bus voltage. In addition, various parameters such as input voltage and DC bus voltage are provided for the drive algorithm to solve the harmonic problem and the DC bus voltage stability problem.

[0025] It should be pointed out that the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A DC busbar small-capacity capacitor frequency conversion control circuit, comprising a rectifier, a DC busbar, a small-capacity capacitor, an inverter and an inverter control module; the two output ends of the rectifier are connected to the DC busbar, and the small-capacity capacitor and the inverter are sequentially connected in parallel with the DC busbar; characterized in that: It also includes a power supply switch, an inverter control module power supply circuit and a power supply control module; The power switch is connected between the rectifier and the AC input; The inverter control module power supply circuit is connected to the AC input to provide power to the inverter control module; The power supply control module is used to control the power supply switch to close after the power supply circuit of the inverter control module operates stably, so that the AC input is connected to the rectifier; The inverter control module power supply circuit includes a first resistor, a first diode, an electrolytic capacitor, a switch tube and a transformer; one end of the first resistor is connected to the AC input, the other end of the first resistor is connected to the positive electrode of the first diode, the negative electrode of the first diode is connected to one end of the primary coil of the transformer, the other end of the primary coil of the transformer is connected to the second input end of the switch tube, the output end of the switch tube is grounded, and the first input end of the switch tube is connected to the positive end of the electrolytic capacitor; The positive terminal of the electrolytic capacitor is connected to the negative terminal of the first diode, and the negative terminal of the electrolytic capacitor is grounded; after the whole machine is powered on, the AC input is half-wave rectified by the first diode after passing through the first resistor to output a pulsating DC, and the pulsating DC output charges the electrolytic capacitor. When the voltage of the electrolytic capacitor reaches a set value, the switch tube performs switch control to supply power to the inverter control module and / or the power supply control module; The DC bus small-capacity capacitor frequency conversion control circuit also includes a DC bus surge voltage absorption circuit. The DC bus surge voltage absorption circuit includes a second diode, a second resistor and the electrolytic capacitor; the positive electrode of the second diode is connected to the first DC output end of the rectifier, the negative electrode of the second diode is connected to the second resistor, and the other end of the second resistor is connected to the negative electrode of the first diode; when the bus voltage rises instantaneously, the DC bus charges the electrolytic capacitor through the second diode and the second resistor, reduces the voltage value of the bus, and maintains the stability of the DC bus voltage; The DC bus small-capacity capacitor frequency conversion control circuit also includes a bus voltage detection circuit; the bus voltage detection circuit is connected to the DC bus and is used to obtain and output the voltage on the DC bus.

2. The DC bus small-capacity capacitor frequency conversion control circuit according to claim 1, characterized in that: The DC bus small-capacity capacitor frequency conversion control circuit also includes a DC bus overvoltage protection circuit; The DC bus overvoltage protection circuit includes a reference voltage circuit and a first comparator; The output of the reference voltage circuit is connected to the first input end of the first comparator, and the second input end of the first comparator is connected to the DC bus or the positive end of the electrolytic capacitor; the output end of the first comparator is connected to the inverter control module; when the DC bus voltage is higher than the output voltage of the reference voltage circuit, the inverter control module stops the inverter output according to the output control of the first comparator.

3. The DC bus small-capacity capacitor frequency conversion control circuit according to claim 1, characterized in that: The DC bus small-capacity capacitor frequency conversion control circuit also includes an AC input voltage detection circuit; The AC input voltage detection circuit includes a resistor network circuit, a bias voltage setting circuit and a second comparator; The input end of the resistor network circuit is connected to the AC input, the first output end of the resistor network circuit is connected to the first input end of the second comparator; the second output end of the resistor network is connected to the second input end of the second comparator; The output of the bias voltage setting circuit is connected to the first input terminal of the second comparator.

4. Frequency conversion equipment, characterized in that It comprises the DC bus small-capacity capacitor frequency conversion control circuit as described in any one of claims 1 to 3.

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