An overcurrent protection system for inverter of shore power system

Abstract

The present invention proposes an overcurrent protection system for an inverter of a shore power system, comprising: a smoothing reactor, a bridge rectifier circuit, a DC filter circuit, an overcurrent protection circuit, an inverter and a sine filter circuit, wherein the smoothing reactor is connected to the input end of the sine filter circuit through the bridge rectifier circuit, the DC filter circuit, the overcurrent protection circuit and the inverter connected in series in sequence. The present invention uses an overcurrent protection circuit to intercept the instantaneous overcurrent generated by high-power electrical equipment during the start-stop process, and converts it into a current that the inverter can withstand, thereby ensuring the safety of the entire frequency conversion system. At the same time, a sine filter circuit is connected behind the inverter, which can convert the PWM waveform output by the inverter into a sine wave, thereby improving the quality of electric energy.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to an inverter overcurrent protection system for a shore power system. Background Art

[0002] Nowadays, after a ship docks, the diesel engine on board still needs to run to ensure the life of the crew and the operation of some equipment on board. However, diesel engines not only consume a lot of energy, but also cause pollution to the surrounding environment. As the concept of green development has become popular, the pollution problem in the port area has attracted much attention from all walks of life. Therefore, the shore power system has become the focus of people's attention.

[0003] The shore power system is a system where, when a ship is docked at a pier, it stops using its own auxiliary generator and instead uses land power to supply power to the main onboard systems. However, the inverter in the shore power system cannot withstand instantaneous overcurrent during the start-up and shutdown of high-power electrical equipment and is damaged. At the same time, instantaneous overcurrent will also affect the power quality. Therefore, how to protect the inverter while improving the power quality has become an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present invention proposes an inverter overcurrent protection system for a shore power system to solve the technical problem that overcurrent generated during the start-up and shutdown process of relatively powerful electrical equipment damages the inverter and reduces the quality of electric energy.

[0005] The technical solution of the present invention is implemented as follows: The present invention provides an inverter overcurrent protection system for a shore power system.

[0006] On the basis of the above technical solution, preferably, a smoothing reactor, a bridge rectifier circuit, a DC filter circuit, an overcurrent protection circuit, an inverter and a sine filter circuit;

[0007] The smoothing reactor is connected to the input end of the sine filter circuit via a bridge rectifier circuit, a DC filter circuit, an overcurrent protection circuit and an inverter which are connected in series in sequence.

[0008] Further preferably, the overcurrent protection circuit comprises: a sliding resistor RP1, capacitors C1-C2, resistors R1-R3 and an operational amplifier U1;

[0009] The output end of the DC filter circuit is connected to the positive input end of the overcurrent protection circuit operational amplifier U1, and the output end of the DC filter circuit is also connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the power supply. One end of the capacitor C1 is connected in parallel with one end of the resistor R1, and the other end of the capacitor C1 is connected in parallel with the other end of the resistor R1. The reverse input end of the operational amplifier U1 is connected to the middle end of the sliding rheostat RP1, and one end of the sliding rheostat RP1 is connected to the power supply and the other end is grounded. The output end of the operational amplifier U1 is connected to the input end of the inverter from the other end of the resistor R2 through one end of the resistor R2, and the other end of the resistor R2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the power supply. The output end of the operational amplifier U1 is also connected to the other end of the resistor R3, and one end of the resistor R3 is grounded.

[0010] Further preferably, the inverter includes: an inductor LIN, inductors L1-L3, a capacitor CIN, capacitors C3-C5, diodes D1-D5 and VSI;

[0011] The output end of the operational amplifier U1 is connected to one end of the inductor LIN of the inverter, the other end of the inductor LIN is connected to one end of the diode D1, the other end of the diode D1 is connected in series with the inductor L1, the diode D2, the diode D3, the capacitor L2 and VSI in sequence, the other end of the inductor L1 is connected to one end of the diode D2, the other end of the diode D2 is connected to one end of the diode D3, the other end of the diode D3 is connected to one end of the capacitor L2, the other end of the capacitor L2 is connected to one end of the VSI, the other end of the diode D1 is also connected to one end of the capacitor CIN, the other end of the capacitor CIN is connected to the other end of the VSI One end of the diode D4 is connected in parallel with one end of the diode D1, and the other end is connected in parallel with the other end of the inductor L2. One end of the capacitor C3 is connected in parallel with one end of the inductor L1, and the other end is connected in parallel with the other end of the diode D2. One end of the capacitor C5 is connected in parallel with one end of the diode D2, and the other end is connected in parallel with the other end of the inductor L2. One end of the inductor L3 is connected in parallel with one end of the diode D3, and the other end is connected to one end of the diode D5. The other end of the diode D5 is connected in parallel with the other end of the inductor L2. One end of the capacitor C4 is connected in parallel with the other end of the diode D3, and the other end of the capacitor C4 is connected in parallel with the other end of the inductor L3. The output end of the VSI is connected to the input end of the sinusoidal filter circuit.

[0012] Further preferably, the VSI comprises: transistors Q1-Q6;

[0013] The other end of the inductor L2 is connected to one end of the transistor Q1, the other end of the transistor Q1 is connected to one end of the transistor Q2, the other end of the transistor Q2 is connected to the other end of the capacitor CIN, the middle end of the transistor Q1 and the transistor Q2 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q3 is connected in parallel with one end of the transistor Q1, one end of the transistor Q3 is connected to the other end of the transistor Q4, the other end of the transistor Q4 is connected in parallel with the other end of the transistor Q2, the middle end of the transistor Q3 and the transistor Q4 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q5 is connected in parallel with one end of the transistor Q3, one end of the transistor Q5 is connected to the other end of the transistor Q6, the other end of the transistor Q6 is connected in parallel with the other end of the transistor Q4, the middle end of the transistor Q5 and the transistor Q6 is the first phase output, connected to the input end of the sine filter circuit.

[0014] Further preferably, the sinusoidal filter circuit comprises: an inductor L4, a capacitor C6 and a resistor R4;

[0015] The output end of the inverter is connected to one end of the inductor L4 of the sine filter circuit, the other end of the inductor L4 is the positive output end, the other end of the inductor L4 is also connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to one end of the resistor R4, and the other end of the resistor R4 is the negative output end.

[0016] The shore power system inverter overcurrent protection system of the present invention has the following beneficial effects compared with the prior art:

[0017] (1) The present invention can intercept excessive instantaneous overcurrent by providing an overcurrent protection circuit and convert it into a current that the inverter can withstand, thereby ensuring the safety of the entire frequency conversion system;

[0018] (2) The sine filter circuit of the present invention can convert the PWM waveform output by the inverter into a sine wave, thereby improving the quality of electric energy, while ensuring that the inverter will not be damaged, and improving the quality of electric energy output by the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the structure of an inverter overcurrent protection system for a shore power system of the present invention;

[0021] Figure 2 A circuit diagram of an overcurrent protection circuit of the present invention;

[0022] Figure 3 is a circuit diagram of an inverter of the present invention;

[0023] Figure 4 4 is a circuit diagram of a sine filter circuit of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0025] like Figure 1 As shown, an inverter overcurrent protection system for a shore power system of the present invention comprises: a smoothing reactor, a bridge rectifier circuit, a DC filter circuit, an overcurrent protection circuit, an inverter and a sine filter circuit, wherein the smoothing reactor is connected to the input end of the sine filter circuit via the bridge rectifier circuit, the DC filter circuit, the overcurrent protection circuit and the inverter which are connected in series in sequence.

[0026] Smoothing reactor, the smoothing reactor is used in the DC circuit after rectification. The number of pulses in the rectifier circuit is always limited, and there is always ripple in the output rectified voltage. This ripple is often harmful and needs to be suppressed by the smoothing reactor. The smoothing reactor and the DC filter together form a DC T-type harmonic filter network, which reduces the AC pulsation component and filters out some harmonics, reduces the interference to communication along the DC line and avoids harmonics from making the regulation unstable.

[0027] Bridge rectifier circuit, used to convert AC power into DC power.

[0028] DC filter circuit, DC filter is a filter mainly used to block and short-circuit AC signals. Capacitors can be used for filtering to make the output waveform smoother, and capacitors can be connected in series to increase the withstand voltage and in parallel to increase the capacity to make the output DC more stable. At the same time, it can suppress harmonics on the DC side of the high-voltage DC transmission system.

[0029] Overcurrent protection circuits are used, for example Figure 2As shown, the overcurrent protection circuit includes: a sliding rheostat RP1, capacitors C1-C2, resistors R1-R3 and an operational amplifier U1; the output end of the DC filter circuit is connected to the positive input end of the overcurrent protection circuit operational amplifier U1, the output end of the DC filter circuit is also connected to one end of the resistor R1, the other end of the resistor R1 is connected to a power supply, one end of the capacitor C1 is connected in parallel with one end of the resistor R1, the other end of the capacitor C1 is connected in parallel with the other end of the resistor R1, the reverse input end of the operational amplifier U1 is connected to the middle end of the sliding rheostat RP1, one end of the sliding rheostat RP1 is connected to the power supply, and the other end is grounded, the output end of the operational amplifier U1 is connected to the input end of the inverter from the other end of the resistor R2 through one end of the resistor R2, the other end of the resistor R2 is also connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the power supply, the output end of the operational amplifier U1 is also connected to the other end of the resistor R3, and one end of the resistor R3 is grounded. Among them, resistor R2 and capacitor C2 form a delay circuit, through which the high level can be changed into a low level. The sliding rheostat RP1, resistors R1 and R3, and capacitor C1 act as a buffer to prevent the instantaneous overcurrent generated by high-power electrical equipment during the start-stop process from damaging the inverter.

[0030] Inverter, such as Figure 3As shown, it is used to convert a DC power supply into an AC power supply with controllable voltage and a frequency of 60Hz. At this time, the voltage waveform is a PWM waveform. The inverter includes: an inductor LIN, an inductor L1-L3, a capacitor CIN, a capacitor C3-C5, a diode D1-D5 and a VSI. The output end of the operational amplifier U1 is connected to one end of the inductor LIN of the inverter, the other end of the inductor LIN is connected to one end of the diode D1, the other end of the diode D1 is connected in series with the inductor L1, the diode D2, the diode D3, the capacitor L2 and the VSI in sequence, the other end of the inductor L1 is connected to one end of the diode D2, the other end of the diode D2 is connected to one end of the diode D3, the other end of the diode D3 is connected to one end of the capacitor L2, and the other end of the capacitor L2 is connected to one end of the diode D3. One end is connected to one end of VSI, the other end of diode D1 is also connected to one end of capacitor CIN, the other end of capacitor CIN is connected to the other end of VSI, one end of diode D4 is connected in parallel to one end of diode D1, and the other end is connected in parallel to the other end of inductor L2, one end of capacitor C3 is connected in parallel to one end of inductor L1, and the other end is connected in parallel to the other end of diode D2, one end of capacitor C5 is connected in parallel to one end of diode D2, and the other end is connected in parallel to the other end of inductor L2, one end of inductor L3 is connected in parallel to one end of diode D3, and the other end is connected to one end of diode D5, and the other end of diode D5 is connected in parallel to the other end of inductor L2, one end of capacitor C4 is connected in parallel to the other end of diode D3, and the other end of capacitor C4 is connected in parallel to the other end of inductor L3, and the output end of VSI is connected to the input end of the sinusoidal filter circuit. Among them, inductor LIN, capacitor CIN, and diodes D1 and D4 constitute a traditional DC / DC boost structure and an improved quasi-Z source network. The improved quasi-Z source network can replace an energy storage inductor with a boost unit to improve the boost capability of the structure.

[0031] For the inverter, the front stage is composed of an inductor LIN, a capacitor CIN and two diodes D1 and D4, which can suppress the current impact at startup, because the DC / DC boost structure will not generate an additional path with the inverter, and the inductor LIN is connected in series with the power supply, which makes up for the defects of the discontinuous quasi-Z source network in the rear stage, making the input current of the Z source inverter continuous while reducing the voltage stress that the capacitors C3 and C5 need to bear. In addition, the energy storage inductor in the quasi-Z source network of the rear stage is replaced by a boost unit, which increases the overall boost capability. Diodes D3, D5, inductors L2, L3 and capacitor C4 constitute a boost unit. In the direct-through state, diodes D3 and D5 are turned on, and the power supply charges the energy storage inductors L2 and L3. In the non-direct-through state, that is, the inverter works normally, diode D2 is turned on, and D3 and D5 are cut off by the reverse voltage. At this time, the energy storage inductors L2 and L3 supply power to the load together, so a higher boost characteristic can be obtained. The structure of the boost unit is the same as that of the switch unit, except that the capacitor C4 is used in the boost unit to replace the diode D2 in the switch unit. The working principle of the boost unit is the same as that of the switch unit. In the through state, the system power supply will charge the energy storage inductors L2 and L3. In the non-through state, in addition to the energy storage inductors L2 and L3, the capacitor C4 is also included to discharge the load together. The three components are connected in series to supply power together, which further increases the DC side voltage of the inverter. Therefore, the improved high-gain Z-source inverter uses a boost unit to replace the energy storage inductor to obtain a higher boost capability.

[0032] Wherein, VSI comprises: transistors Q1-Q6, the other end of the inductor L2 is connected to one end of the transistor Q1, the other end of the transistor Q1 is connected to one end of the transistor Q2, the other end of the transistor Q2 is connected to the other end of the capacitor CIN, the middle end of the transistor Q1 and the transistor Q2 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q3 is connected in parallel with one end of the transistor Q1, one end of the transistor Q3 is connected to the other end of the transistor Q4, the other end of the transistor Q4 is connected in parallel with the other end of the transistor Q2, the middle end of the transistor Q3 and the transistor Q4 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q5 is connected in parallel with one end of the transistor Q3, one end of the transistor Q5 is connected to the other end of the transistor Q6, the other end of the transistor Q6 is connected in parallel with the other end of the transistor Q4, the middle end of the transistor Q5 and the transistor Q6 is the first phase output, connected to the input end of the sine filter circuit.

[0033] Sine filter circuit, such as Figure 4As shown, the sine filter circuit includes: an inductor L4, a capacitor C6 and a resistor R4, the output end of the inverter is connected to one end of the inductor L4 of the sine filter circuit, the other end of the inductor L4 is a positive output end, the other end of the inductor L4 is also connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to one end of the resistor R4, and the other end of the resistor R4 is a negative output end. Among them, the inductor L4, the capacitor C6 and the resistor R4 constitute an RLC second-order low-pass filter, which is used to convert the PWM waveform output by the inverter into a sine wave, thereby improving the quality of electric energy. In this embodiment, the sine filter circuit is a three-phase sine filter circuit, which is respectively connected to the three-phase output of the inverter.

[0034] The specific implementation of the present invention is as follows: a DC T-type harmonic filter network is formed by a smoothing reactor and a DC filter to reduce the AC pulsating component and filter out some harmonics, and then a 50Hz AC power supply is converted into a DC power supply through a rectifier, and then the DC power supply is suppressed through an overcurrent protection circuit to protect the inverter, and then the DC power supply is converted into a voltage-controllable AC power supply with a frequency of 60Hz through an inverter, and finally filtered and output through a sine wave filter circuit.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A shore power system inverter overcurrent protection system, characterized in that: include: Smoothing reactor, bridge rectifier circuit, DC filter circuit, overcurrent protection circuit, inverter and sine filter circuit; The smoothing reactor is connected to the input end of the sine filter circuit via a bridge rectifier circuit, a DC filter circuit, an overcurrent protection circuit and an inverter which are connected in series in sequence; The overcurrent protection circuit includes: a sliding resistor RP1, capacitors C1-C2, resistors R1-R3 and an operational amplifier U1; The output end of the DC filter circuit is connected to the positive input end of the overcurrent protection circuit operational amplifier U1, and the output end of the DC filter circuit is also connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the power supply, one end of the capacitor C1 is connected in parallel with one end of the resistor R1, and the other end of the capacitor C1 is connected in parallel with the other end of the resistor R1, the reverse input end of the operational amplifier U1 is connected to the middle end of the sliding variable resistor RP1, one end of the sliding variable resistor RP1 is connected to the power supply, and the other end is grounded, the output end of the operational amplifier U1 is connected to the input end of the inverter from the other end of the resistor R2 through one end of the resistor R2, the other end of the resistor R2 is also connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the power supply, the output end of the operational amplifier U1 is also connected to the other end of the resistor R3, and one end of the resistor R3 is grounded; The inverter includes: an inductor LIN, inductors L1-L3, a capacitor CIN, capacitors C3-C5, diodes D1-D5 and VSI; The output end of the operational amplifier U1 is connected to one end of the inductor LIN of the inverter, the other end of the inductor LIN is connected to one end of the diode D1, the other end of the diode D1 is connected in series with the inductor L1, the diode D2, the diode D3, the capacitor L2 and VSI in sequence, the other end of the inductor L1 is connected to one end of the diode D2, the other end of the diode D2 is connected to one end of the diode D3, the other end of the diode D3 is connected to one end of the capacitor L2, the other end of the capacitor L2 is connected to one end of the VSI, the other end of the diode D1 is also connected to one end of the capacitor CIN, the other end of the capacitor CIN is connected to the other end of the VSI One end of the diode D4 is connected in parallel with one end of the diode D1, and the other end is connected in parallel with the other end of the inductor L2; one end of the capacitor C3 is connected in parallel with one end of the inductor L1, and the other end is connected in parallel with the other end of the diode D2; one end of the capacitor C5 is connected in parallel with one end of the diode D2, and the other end is connected in parallel with the other end of the inductor L2; one end of the inductor L3 is connected in parallel with one end of the diode D3, and the other end is connected to one end of the diode D5; the other end of the diode D5 is connected in parallel with the other end of the inductor L2; one end of the capacitor C4 is connected in parallel with the other end of the diode D3, and the other end of the capacitor C4 is connected in parallel with the other end of the inductor L3; the output end of the VSI is connected to the input end of the sinusoidal filter circuit; The VSI includes: transistors Q1-Q6; The other end of the inductor L2 is connected to one end of the transistor Q1, the other end of the transistor Q1 is connected to one end of the transistor Q2, the other end of the transistor Q2 is connected to the other end of the capacitor CIN, the middle end of the transistor Q1 and the transistor Q2 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q3 is connected in parallel with one end of the transistor Q1, one end of the transistor Q3 is connected to the other end of the transistor Q4, the other end of the transistor Q4 is connected in parallel with the other end of the transistor Q2, the middle end of the transistor Q3 and the transistor Q4 is the first phase output, connected to the input end of the sine filter circuit, one end of the transistor Q5 is connected in parallel with one end of the transistor Q3, one end of the transistor Q5 is connected to the other end of the transistor Q6, the other end of the transistor Q6 is connected in parallel with the other end of the transistor Q4, the middle end of the transistor Q5 and the transistor Q6 is the first phase output, connected to the input end of the sine filter circuit; The sinusoidal filter circuit includes: an inductor L4, a capacitor C6 and a resistor R4; The output end of the inverter is connected to one end of the inductor L4 of the sine filter circuit, the other end of the inductor L4 is the positive output end, the other end of the inductor L4 is also connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to one end of the resistor R4, and the other end of the resistor R4 is the negative output end.

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